How do Plants do this

[action1a9]

How can such a delicate plant such as a Thistle, and other plants grow under say 2 inches thick Tarmac / Concrete lift up through the Tarmac / Concrete breaking it up in the process. ??
Derek

[Chillum]

don't know, but it's always impressed me immensely.

[peanut]

i'm pretty sure its not the plant that breaks the concrete. concrete ususlly cracks due to expansion and other forces of nature. once the concrete is cracked it lets light through the crack. since plants grows towad the light and in the path of least resistance, it goes through the crack. so basically the plant does not start to grow until after the concrete is cracked.

[action1a9]

yes can  understand it growing out of cracks in Concrete but Tarmac without Cracks ? and lift the whole thing up till it push out.

[firefly]

Carbon dioxide can pass through concrete into the soil. Of course it couldn't develop leaves under the concrete due to photosynthesis.

[Woodstock]

I had this conversation once with a land surveyor involved in the building of roads, and he said it was a known fact that some plants, such as thistles, actually thrived on a particular chemical found in bitumen which made them stronger than ever.  Not sure how "known" that fact really is, but it does sound plausible.