A NGIOSPERMS. DICOTYLEDONS. 



447 



Ranunculus Ficaria *, where it is sheathing below, and in Carum Bulbocastanum, in 

 which, as Hegelmaier 2 has shown, the pseudo-monocotyledonous form of the embryo, 

 that is the presence of an apparently single terminal cotyledon, is due to the almost 

 complete abortion of one cotyledon, the other being usually lateral in its origin. 

 A similar explanation probably applies to Ranunculus Ficaria also, and to 

 Bulbocapnos, a section of Corydalis. The two cotyledons usually form much the 

 largest part of the mature embryo, so that the axis appears as a small conical 



D 



FIG. 373. Ricinus communis. / the ripe seed cut through 

 longitudinally. // the young plant with the cotyledons still fixed 

 in the endosperm, as shown more distinctly in A and B. s the 

 seed-coat, <? endosperm, c cotyledon, he hypocotyl, v> primary root, 

 w 1 its secondary roots, x caruncule characteristic of the Euphor- 

 biaceae. 



FIG. 376. Vicia Faba. A a seed after re- 

 moval of one of the cotyledons, the other c being 

 retained ; iu extremity of the root, kn plumule, 

 s seed-coat. B seed germinating ; j seed-coat, / a 

 lobe of the seed-coat torn away, n hilum, st stalk of 

 a cotyledon, k curvature of the epicotyledonary 

 portion of the axis, i, he the very short hypocotyl, 

 h the primary root, TVS its tip, Kn bud axillary to 

 one of the cotyledons. 



appendage between them ; this is most striking when the embryo attains a very 

 considerable absolute size in a seed without endosperm and the cotyledons swell up 

 into two thick fleshy bodies, as in Aesculus, Castanea, Quercus (Fig. 379), Amygdalus, 

 Vicia Faba, Phaseolus, Bertholletia excelsa and many others ; but in most cases 

 the cotyledons are thin and resemble shortly stalked foliage-leaves of simple form, 

 as in Cruciferae, Euphorbiaceae and Tilia, in which last the lamina has from three 

 to five lobes; they often have their inner faces laid flat on one another (Figs. 375, 

 376), but are sometimes folded or wrinkled, as in Theobroma with thick cotyledons, 

 Acer, the Convolvulaceae and others with thin ones; they are less often wound 

 spirally round one another (convolute) (Fig. 374). 



The axis of the embryo beneath the cotyledons is usually of an elongate conical 

 shape, and in this form is termed the radicle in books of descriptive botany ; but the 



1 Irmisch, Beitr. z. vergl. Morphol. d. Pflanzen, Halle, 1854, p. 12. 



2 Vergl. Untersuchungen, Stuttgart, 1875. 



