The three of them could clearly feel that the ground beneath their feet was shaking slightly.
"The roots of the World Tree can also take root in the underground world..."
Xu Xin muttered to himself as he looked at the magnificent scenery in front of him that he had helped to create.
"That's right, but it can't spread as far as above ground." Xu Ying said with some regret, "After all, there is a soilless area up to three thousand meters vertically in this underground world. The roots of the World Tree can penetrate into the ground of the underground world like this, which is almost the limit."
"Can't the roots of the World Tree extend to areas hundreds of kilometers away?" Li Wenxi felt the vibration under his feet. "If there is no such hollow underground world, can its roots extend all the way down?"
"I'm not sure about this, but judging from the situation above, it will at least be deeper."
Xu Ying looked up at the dome.
The intricate root system filled the dome above the people.
These roots have drilled out of the dome, and countless roots have covered the entire dome, as if expressing their dissatisfaction.
They still want to drill down, but there is no soil, rocks, etc. for them to drill into.
The ground under my feet was still shaking, but the giant beasts and insects on the ground were no longer as panicked as before. Instead, they calmed down and lay on the ground one by one, as if they were feeling something.
The three were also waiting for the shaking to stop and for the roots to cover the area.
“Hey, you guys think, this underground world can’t be spread all over the world, right?” Li Wenxi asked the question that was in his mind.
"Hmm? They're all over the world, right?" Xu Ying turned to look at her and said, "There shouldn't be any problem with that, right?"
"In that case... what is supporting the ground?" Li Wenxi stretched out her slender fingers and pointed upwards.
"Ah, you're talking about that. There must be support." Xu Ying explained, "Although the underground world is all connected, there is a 'support column' every few meters that is more magnificent than a mountain and has a diameter of at least tens of kilometers, or even hundreds of kilometers, so there is no need to worry about that."
Xu Xin imagined it.
The "support column" has a diameter of hundreds of kilometers and a vertical height of only three thousand meters...
It would be more appropriate to call it a "support plate" rather than a "support column".
A stepping stone of the Earth's crust
He looked around.
Unfortunately, in this underground world, only this area has some light, and the source is the light source where the main vine bundle connects to the dome.
Further away, it was pitch black.
Even if he ate a red berry, he still couldn't see too far away.
"No need to look around, there are none here." Xu Ying reminded, "If we calculate based on the distance on the ground, there is at least one support column every 2,000 kilometers."
Why do we say "calculated based on the ground distance"? Because the underground distance is different from the ground distance.
The underground world is closer to the center of the earth. If we calculate the distance of the underground world, it must be shorter than 2,000 kilometers.
"Two thousand kilometers? That's really far..." Li Wenxi said in surprise, "If the Earth hadn't gotten bigger, there probably wouldn't be many of them on the entire Earth, right?"
"That's not the case." Xu Xin calculated, "The equator is more than 40,000 kilometers long. There are more than 20 of them on the equator alone, and there are even more if you count them on the entire planet."
But now, the surface area of the earth has expanded a hundred times.
At first glance, these support pillars seem to be very far apart, with each one being as much as two thousand kilometers. In fact, considering the size of the entire earth today, they are very densely distributed.
No wonder the entire earth's crust and the world above ground can be supported.
Xu Ying pointed upwards and said, "This is the location we specially selected. It is very far from each of the 'support pillars'. The nearest support pillar is nearly a thousand kilometers away."
"Why do we have to be as far away from each support pillar?" Xu Xin was puzzled. "Why do we have to stay away from the support pillars?"
"Yes!" Li Wenxi imagined the appearance of the support column. "If we plant the World Tree on the 'support column', then wouldn't the roots of our World Tree be able to extend downwards? That World Tree should be stronger!"
"That's right." Xu Ying pursed her lips and said, "But, if we can think of this, how can the other party not think of it?"
"The other party...ah." Xu Xin understood immediately: "You mean, the world trees of those alien invaders are actually planted on the 'support pillars'?"
Xu Ying nodded: "Yes, that's right. The world tree planted on the 'support pillar' will not only affect a large area on the ground, but the roots will also extend downward from the 'support pillar' and continue to spread into the ground of the underground world. In that case, only one world tree is needed, and they can easily control large areas of the ground world and the underground world."
As she spoke, there was a hint of helplessness in her tone: "This is how those alien invaders occupied the earth."
"They first developed world tree seeds that they could carry with them, took these seeds to find the 'support pillars', and then planted them. In this way, their rule could continue to expand in both the surface and underground worlds. Now, they have occupied half of the earth."
Xu Xin and Li Wenxi looked at each other and could see the shock in each other's eyes.
This method... is convenient and fast, there is no other solution!
It is just like a country on Earth thousands of years ago, planting its flag on an area to indicate that this area is their territory.
And then they didn't have to do anything, because the flag helped them occupy this area! And even occupied the underground world!
This is really...
"... Wait a minute, wait a minute. I remember you said before that the range of influence of the World Tree is only a few hundred kilometers, right?" Li Wenxi suddenly asked.
"Well, normally it's about 500 to 600 kilometers in radius." Xu Ying nodded.
"But the distance between those 'support pillars' is at least 2,000 kilometers." Xu Xin pondered, "That is to say... there is a large area between the two world trees that is not affected by them."
"Bingo!" Xu Ying clapped her hands, "That's right!"
"In simple terms, it's similar to the safe zone in your tree house. The area affected by the World Tree is the 'safe zone' for alien invaders, and the area not affected is their 'danger zone'.
"We are now in the enemy's 'danger zone', and we are in the core area of the 'danger zone'. We chose to build Crystal City here because of its location."
Xu Ying has explained it very clearly.
"It turns out to be like this..." Xu Xin whispered to himself.
It seems that perhaps all of them who survived are in the "danger zone" that is not affected by the World Tree.
Because the world tree will obviously affect the growth, ownership and transplantation of the tree house.
In order to eliminate this factor and select the survivors, they will definitely not choose to let the survivors play this survival game within the influence of the World Tree.
Of course, it may also be because they don't want the survivors, these "insects", to get too close to them.
In any case, the current survivors should be considered lucky, at least they are not under the control of the other side's world tree.
"Well, that means there is a World Tree nearly a thousand kilometers away from us?" Li Wenxi asked, "Then... it's not that far away."
It was almost the distance between the Imperial Capital and the Demonic Capital on Earth a thousand years ago.
"Yes." Xu Ying nodded, "But when we were building Crystal City, they basically didn't care about this place."
"Not much? Why?"
"Because those alien bastards mainly live on that half of the planet. That's the place Shi Wanyun visited."
Xu Ying squatted down and touched the ground, feeling the increasingly weak vibrations under her feet, and said, "The underground world is so rich in resources, and the number of alien invaders is not large. They don't have any population pressure, and they don't lack survivor research resources. There is no need to spend energy on expansion to occupy large areas of useless area."
Xu Xin was silent for a moment and said, "But now... we can't be so optimistic."
They have already planted a world tree here!
Relying on this world tree, they own their own territory and have the ability to compete with the opponent.
Now this place must have become their key focus area.
"Then...what if the other party plants another World Tree around our World Tree in order to restrict us?" Li Wenxi proposed a hypothesis, "Will it compete with our World Tree for territory and affect us?"
"Not as far as I know." Xu Ying stood up and said, "As far as I know, the World Tree follows the principle of first come, first served. This area has been occupied by our World Tree. Other World Trees can't even grow on this land, unless they are... 'parasitic'. This is the 'protected area' of the World Tree."
"And if we plant a new world tree outside the 'protected area', according to the 'first come, first served' principle, the roots of the later planted world tree will not be able to spread here. At most, the 'protected areas' of the two world trees will be connected together."
As she spoke, she smiled and said, "You should be quite familiar with this. It's actually similar to your tree house. The tree house is a degraded version of the World Tree. The properties of the two are basically the same."
ah.
That's true.
But they still don't know much about the details.
After all, they only knew that the safe area of the tree house was connected. At that time, there was no danger zone in this area. What was the "first come, first served" principle? Who knew how the roots of the tree house below were distributed
Xu Ying's explanation allowed the two of them to know a lot of details.
"The vibration has stopped." Xu Ying smiled, "Now, this area is our territory!"
"Where are those giant beasts?" Xu Xin asked.
"If they dare to attack us, just kill them!"
As she spoke, Xu Ying waved her hand upwards.
In an instant, a thick root with a sharp tip emerged from the ground!
These thick roots could probably cause considerable damage to the giant beast!
"Ah!" Li Wenxi was so surprised that his mouth opened wide. "You can control those roots!"
"Hehe, that's right! My brother can do it too."
Xu Xin is already trying.
"Card!"
A thick root broke out of the ground along with his consciousness!
"Success!" Xu Xin's eyes flashed with shock. He turned to look at Xu Ying, "Then can it be done on the ground as well..."
"Of course, but the controllable range is not that large. It's probably just the area covered by the crown of the World Tree." Xu Ying thought for a while and said.
That's already very strong!
The canopy of the World Tree has basically covered the entire Crystal City now, right
He was excited, and another thick and sharp root emerged from the ground!
Several giant insects on the ground were directly blown away!
So strong!
"Um… "
Xu Xin suddenly frowned.
He felt tired.
It's coming fiercely, sweeping over like a wave!
Even his feet felt a little weak.
Li Wenxi also quickly supported him and asked nervously: "What's wrong? Why did you suddenly..."
"Ah, you need to exercise moderation, brother!"
Xu Ying also hurried over to support him.
"You just controlled the roots of the dome, and now you have controlled it twice in a row. You should have reached your limit, right? It is not that easy to control the World Tree. My super-mutated physical strength and more than three hundred years of mental strength are already exhausted."
Xu Xin is indeed exhausted both physically and mentally now.
Including the time he had just controlled the dome's roots to drill downward, he had controlled the World Tree's roots to move seven times in total.
This number of times is enough!
Xu Xin smiled.
Although he was physically tired, he was in a good mood.
"Still smiling! You look so pale!" Li Wenxi supported Xu Xin and turned to look at Xu Ying, "Are you tired or injured?"
"I'm just tired. My body is overdrawn." Xu Ying was not worried. "I'll be fine after a rest."
"No need." Xu Xin took out a few blue-level fruits and started eating. "It will be fine after a while of recovery. Can we go over there and take a look now?"
Xu Xin looked at the main vine bundle.
Surrounded by dozens of world tree roots, the main vine is still the most conspicuous.
It is much thicker than the roots of the dozen or so world trees around it!
It is even thicker than the main trunk of the World Tree.
"Well, go check it out. It's safe now."
As she spoke, she grabbed their hands and teleported again.
The three of them reached the main vine in an instant.
"Your teleportation is really convenient..." Xu Xing exclaimed.
"Hmm? Wait, can't you teleport to a place you haven't been to?" Li Wenxi suddenly thought of this and felt a little strange. "You just teleported us directly to the underground world, right?"
At the beginning, Xu Ying couldn't even teleport from the ground of the underground world to the dome, a distance of 3,000 meters.
From the ground to the underground world, it is much farther than three thousand meters.
"Normally, it won't work. But this place is affected by the World Tree." Xu Ying opened her eyes wide and looked closely at the main vine bundle, while explaining, "I am teleporting in my own home, how can there be any problems?"
"Ah... That's true!"
"Let's go in and take a look." Xu Ying said as she grabbed their hands again.
Transmit.
Directly entered the underground prison.
The familiar metal prison, the familiar downward spiral staircase.
"Oh, this is the underground prison!"
Xu Ying looked at this huge underground prison that spiraled downward and was secretly surprised.
"Is this all meteorite iron? It's all meteorite iron! Those alien bastards are really extravagant..."
Li Wenxi tugged at Xu Xin's sleeve: "Xu Xin, is this the prison you mentioned? But... why are all these cells empty?"
Xu Xin was also in deep doubt at this time.
He thought that as soon as they came in, they would be able to hear the noisy chirping of the giant insects in the prison.
Because the last time they left, this place was full of giant insects and beasts.
result…
Empty
It's empty.
The entire underground prison, the cells that originally held the violent beasts, now...
There is no beast!
At a glance, it was completely empty, without a single mutant creature.
Where have all those mutant creatures gone