COTYLEDONS. 



599 



and their role of nurse is at an end. Often, indeed, the cotyledons take on 

 later another function, but they have ceased to be of importance as reserve- 

 tissue for the use of the developing embryo. In those instances where the 

 supply of food given by the parent plant is not stored up in the cotyledons, 



Fig. 141.— Cotyledons. 



Longitudinal section of seed of Rieinus, parallel to the plane of the embryo. 2 Longitudinal section of the same seed, taken 

 at right angles to the two parallel cotyledons, s Longitudinal section through a grain of "Wheat {Triticum vulgare); x 4. 

 * Longitudinal section through a grain of Wheat after germination has taken place ; x 4. * The embryo with its soutellum 

 in a grain of Wheat ; x 80. « Absorbent cells on the surface of the soutellum of a grain of Wheat ; x 210. 1 Germinating 

 seed of the Corn-cockle (Agrostemma Oithago); slightly magnified. 8 Longitudinal section of the same. 9 Seedling of the 

 Corn-cockle in a later stage of development. 10 The same in longitudinal section, n Absorbent cells on the surface of 

 the cotyledon adjoining the reserve-tissue in the seed of the Corn-cockle; x 210. '2 Germinating seed of Tradescantia 

 Virginica; slightly magnified, is xhe same in a later stage of development. 1* Transverse section through the knob- 

 like end of the cotyledon of Tradescantia Virginica embedded in the reserve-tissue ; x 10. i' Absorbent cells on the 

 surface of this knob-like end ; x 180. is Germinating seed of the Onion (Allium Cepa): natural size, i' The same cut in 

 half ; slightly magnified. '8 Seedling of the Onion in a later stage of development ; natural size. i9 The same cut through 

 longitudinally ; slightly magnified. 



but is deposited as a special reserve near the embryo, its nourishment is more 

 complicated. 



In this state of affairs the cotyledons have an essentially different function. 

 They serve as agents, and their first task is to take up the building-materials. 

 These have been liquefied in the reserve -tissue, either by changes in that tissue 

 itself, or by the direct solvent action of the cotyledons. They are then conducted 



