POLYGOXACE^E 437 



half by the cotyledons. In transverse section the latter are 

 seen to be twisted in the form of the letter S, with endosperm 

 occupying the sinus. They are deeply but unequally auricled 

 at the base, and the two halves of the lamina are unequal, and 

 the whole therefore unsymmetrical for the same reason as in 

 Geranium. The larger halves are outermost and hug the testa, 

 closely following two out of the three angles of the seed and 

 enclosing the smaller halves. The latter retain their smaller 

 size after germination. The radicle is large, fusiform, and 

 completely enclosed by the folds of the cotyledons. 



The cause of the inequality in the two halves and of the 

 auricles of the cotyledons is as follows : 



The embryo in the young state becoming too wide for the 

 interior of the seed, becomes first folded together longitudinally, 

 and growth continuing the cotyledons become spirally con- 

 volute, forming a large open spiral with all the intermediate 

 spaces filled with the white floury endosperm. The coty- 

 ledons at length get outside the endosperm and direct their 

 course into two out of the three angles of the seed, thus 

 obtaining the greatest possible width. Looking from the apex 

 of the seed that is, from the radicular end of the embryo to the 

 lower end of the seed the cotyledons are after the first folding 

 both twisted in the same direction, from right to left, or in the 

 opposite direction to the course of the sun, or this direction 

 may be reversed. In consequence of this one half of each 

 cotyledon is enclosed by the corresponding half of the other, so 

 that the outer half of each has more room to develop, and is 

 both larger and has larger auricles. 



Seedlings. The cotyledons vary greatly in size and shape, 

 sometimes even in the same genus. Those of Pterostegia 

 drymarioides are rotund, obtuse, entire, and petiolate with a 

 lamina 6'5-7'5 mm. long and the same in width. In the 

 case of Polygonum sphaerostachyum they are rotund, tri- 

 nerved, and taper slightly at the base into short petioles, 

 connate at the base, forming a cup round the axis. The 

 cotyledons of Piurnex Bucephalophorus are narrowly ovate- 

 oblong ; and the two primary leaves are oval. The coty- 

 ledons of a species of Himalayan Eheum from the Saharanpur 

 gardens (N.W. India) are large, foiiaceous, ovate-oblong, and 



