446 PART III. THE CLASSIFICATION OF PLANTS. 



stem bearing the cotyledon or cotyledons, but not projecting be- 

 yond them, termed the hypocotyl, passing posteriorly into (c) the 

 primary root or radicle. In some plants (e.g. Triticum and other 

 Grasses, Phaseolus, Vicia, Amygdalus, etc.) the primary stem has 

 elongated beyond the insertion of the cotyledon or cotyledons, 

 and bears the rudiments of future foliage-leaves : this portion of 

 the primary shoot is termed the plumule or epicotyl. 



The size and texture of the cotyledons vary with the functions 

 which they have to perform. When, as in exalbuminous seeds, 

 such as peas and beans, the cotyledons are themselves the store- 

 houses in which food is deposited for the nutrition of the embryo 

 during its extra-seminal development, they are relatively large, 

 thick, and fleshy; but when, as in albuminous seeds (e.g. Ricinus, 

 Grasses, etc.), the food is stored in the endosperm, the cotyledons 

 are absorbent organs and, though still relatively large, are not 

 thick and fleshy. 



In a few Phanerogams (e.g. Utricularia, which never developes 

 any root, Ruppia rostellata, Wolffia arrhiza) no primary root is 

 developed or even indicated. 



The extra- seminal development of the embryo may be briefly 

 stated as follows : The first event is the elongation of the hypo- 

 cotyl, with the result that the radicle passes, through the micropyle, 

 out of the seed into the soil, where it becomes firmly attached: 

 when (as in some Gymnosperms, Grasses, Tropseolum) the growing- 

 point of the root is developed deep in the tissue of the embryo, 

 the radicle, before it can escape from the seed, has to penetrate 

 this more or less considerable mass of tissue which can be seen, 

 on examining the germinated seed, as a collar, termed the 

 coleorhiza, surrounding the base of the radicle. The other mem- 

 bers then escape from the seed, the coat of which becomes more 

 or less split. In those cases in which the growth of the hypocotyl 

 is active, the cotyledons appear above the surface of the soil, that 

 is, they are epigean (e.g. Cucurbita, Ricinus, Radish, Sunflower, 

 Scarlet Runner, etc., most Gymnosperms), either leaving the seed- 

 coat in the soil, or carrying it up to the surface. In those cases in 

 which the growth of the hypocotyl is comparatively slight, the 

 cotyledons do not reach the surface of the soil, that is, they are 

 hypogean (e.g. Vicia Faba, Pea, Grasses, etc.) : here it is the 

 epicotyl (plumule) which grows rapidly, and is the first member 

 to appear above ground. The part which first appears above 

 ground, whether it be hypocotyl, epicotyl, or cotyledon, usually 



