22 



SEEDLINGS. 



[section 3. 



whole surface. Tt supplements the nutritive matter contained in the 

 embryo. Both together form no large store, but sufficient for establishing 

 the seedling, with tiny root, stem, and pair of leaves for initiating its 

 independent growth; which in due time proceeds as in Pig. 44, 45. 



34. Smaller embryos, less developed in the seed, are more dependent 

 upon the extraneous supply of food. The figures 46-53 illustrate four 



grades in this respect. The smallest, that of the Peony, is still large enough 

 to be seen with a hand magnifying glass, and even its cotyledons may be 

 discerned by the aid of a simple stage microscope. 



35. The broad cotyledons of Mirabilis, or Tour-o'clock (Fig. 52, 53), 

 with the slender caulicle almost encircle and enclose the floury albumen, 

 instead of being enclosed in it, as in the other illustrations. Evidently 

 here the germinating embryo is principally fed by one of the leaf-like coty- 

 ledons, the other being out of contact with the supply. In the embryo of 

 Abronia (Fig. 54, 55), a near relative of Mirabilis, there is a singular 

 modification ; one cotyledon is almost wanting, being reduced to a rudi- 

 ment, leaving it for the other to do the work. This leads to the question 

 of the 



36. Number of Cotyledons. In all the preceding illustrations, the 

 embryo, however different in shape and degree of development, is evidently 



Fig. 44. Seedling of Morning Glory more advanced (root cut away); cotyledons 

 well developed into foliage-leaves: succeeding internode and leaf well developed, 

 and the next forming. 45. Seedling more advanced; reduced to much below 

 natural size. 



