22 



SEEDLINGS. 



[section 3. 



whole surface. It 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 Eig. 44, 45. 



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

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



grades in this respect. The smallest, that of the Peony, is stiU krge enoi^h 

 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 MirabUis, or Four-o'clock CPig- 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 (Eig. 54, 55), a near relative of MirabiUs, 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 



Fia 44. Seedling of Morning Glory more advanced (root out away); cotyledons 

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

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

 natural size. 



