76 minutf: marvels of nature 



the autumn. And when we speak of the " fall of 

 the leaf" it must not be supposed that the leaves 

 fall off by accident or because the frost has nipped 

 them. The tree has arranged for this fall long 

 beforehand. If we examine the scar where a 

 leaf has recently fallen, we find that it is carefully 

 protected by a layer of cork or bark-like cells, so 

 that no open wound is left into the internal tissues 

 of the plant. 



Fig. 50 shows a section through the portion of 

 a Virginian creeper's stem, where a leaf-stalk joins 

 it, just before the leaf would have fallen. It will 

 be seen how the outer bark-like cells had severed 

 the darker vascular bundles or veins, which go 

 into the leaf, and had continued their protective 

 covering between the leaf-stalk and stem, in readi- 

 ness for the separation which was about to take 

 place. Above this is seen, in section, the bud 

 which had formed in the axil of the leaf, and which 

 would have remained as such until the following 



o 



spring, when it would have developed into a new 

 branch of the plant. 



But from the time that the leaf expands in 

 spring until it falls in autumn or, in the case of 

 evergreens, in the following summer, it never 

 ceases during the hours of sunlight to accumulate 

 carbon for the plant. It is a familiar fact to every 

 one, almost, that our atmosphere is always be- 



