22 



THE GROWTH OF THE TP 



of its stem the root begins to grow and t a firm hold on 



the nourishing soil. 



This rudimentary plantlet, as has been already said, can be 

 readily seen by cutting open the seeds of a maple tree, it being 

 one accessible to many, and the horse-chestnut seeds also show 

 it in another of its numerous forms. To see something of cell 

 formation, it is only necessary to magnify the young stem or 

 leaves of a plant, or better still the young root ends which, 

 being more transparent, are, for the purpose, admirable. 



The growth of the tree, therefore, is in two directions. The 

 stem, or trunk, grows uprightly, elongates and sends forth 

 branches to uphold as large a surface of foliage as possible which 

 drinks in abundantly desired gases from the air and assimilates 

 also the nourishment the roots have absorbed from the soil. 

 The roots in another way seek to lengthen themselves in the 

 pliable soil and assiduously to avoid the light of day. 



When the hypocotyl, or little stem of the embryo, has suffi- 

 ciently grown to bear above the two seed leaves, we notice that 

 it continues to elongate, and that between the cotyledons two 

 tiny buds, or the plumule, appear on this newly formed stem. 

 They foretell the second pair of leaves and we may regard 

 them as having been raised on the stem's second joint. In 

 shape they resemble more closely that of the regular foliage of 

 the tree than do the cotyledons which in outline are always 

 very simple. In some plantlets, even before germination, we 

 find between the cotyledons these little buds or forerunners of 

 the second pair of leaves. {Plate /.) 



To elongate the stem, therefore, joint by joint, and to unfold 

 the leaves that it bears at the summit is the manner of upward 

 growth ; and it is by this untiring and unchanging repetition 

 of itself that the little plantlet becomes a tree. 



The growth of the root is in a different way. At the begin- 

 ning, as we have seen, the root was a new growth from the base 

 of the hypocotyl ; and so throughout its entire course of ex- 

 istence, it is new growth that proceeds from the extremities. 



