12 



MORPHOLOGY 



After this is consumed and in good part converted into struc- 

 ture, the plantlet must by the action of its root and leaves imbibe 

 from the soil and air appropriate materials, and 

 assimilate them into nourishing matter needful 

 for further growth. Only then does the rudi- 

 ment of new structure appear, in the form of a 

 growing point, or bud, at the node or apex of 

 the primitive stemlet, between the two seed- 

 leaves. In this case it soon shows itself as 

 a second pair of leaves, at first resting on 

 the node (Fig. 9), next as somewhat upraised 

 by the development of the second internode 

 (Fig. 10, summit), and finally both this inter- 

 node and the pair of leaves complete their 

 growth (Fig. 11). Then the terminal bud 

 which crowns the second node develops in 

 the same way the third pair of leaves and 

 their supporting internode or joint of stem 

 (Fig. 12) ; and so on. 



24. The root and the stem grow not only 

 in opposite directions, but in a different mode. 

 The primordial stem, pre-existing in the seed 

 (though at first it may be extremely short) 

 grows throughout its whole length, but most 

 in its upper part, so that it may become a 

 stemlet two or three inches long. But, soon 

 attaining its full growth as to length, the 

 stem is carried upwards by the subsequent joints or portions, 

 similarly developed and elongated, one after the other. Not 

 that each portion necessarily waits until the growth of its prede- 

 cessor is complete, though this occurs at first in seedling Maples 

 and other embryos unprovided with much store of food, yet the 

 development follows this course and order of succession. The 

 root, on the contrary, cannot be said to pre-exist in the seed, or 

 at most it may be said to exist potentially in tissue of the caulicle 

 from which a root or roots normally originate. 1 It is formed 



1 Yet from nothing which is special to this part of the embryo, nor to the 

 embryo at all. The primary root is developed from subjacent tissue of the 

 tip of the caulicle, just as it is sometimes developed from along the sides, 

 and as secondary roots are from all or most stems under favoring conditions. 

 This complete similarity, and the fact of what is called the " endogenous " 

 origin of roots (i. e. their springing from subjacent rather than superficial 

 tissue) appear fully to warrant the statement in the text above. 



FIG. 10. Maple plantlet with second internode developing. 11. Same with second 

 internode and pair of leaves complete, and bud of the third apparent. 



