44 ON SEEDLINGS 



are not folded ; so that the whole, not the half, of each 



cotyledon corresponds to the form of the seed. 



In the Bignoniacese, again, a large number of species have 



emarginate cotyledons ; and this would appear also, as for 

 instance in Pithecoctenium Aubletii, to 

 be due to the chalaza, though in a 

 different manner. The seeds them- 

 selves are transversely oblong, much 

 compressed dorsally, surrounded on 

 all sides except the base by an ex- 

 tremely thin, transparent, membranous 

 wing, which is traversed by nerves 

 radiating from the central part of the 

 testa, and is uneven at the margin. 

 The raphe is ventral, extending from 

 the hilum to the centre of the embryo. 

 The chalaza is attached to the embryo- 



PIG. 86. Seedling of cheir- sac a little above the middle of the 



anthus Cheiri. Two-thirds , m i j- i 11 



nat . size. embryo. The radicle is very small, 



distant from, but pointing to, the 



hilum. The embryo is straight and flat ; the cotyledons grow 

 until they come to the point of attachment of the chalaza, 

 when they extend forwards on each side, forming two lobes. 



In Oroxylum indicum the general structure of the seed is 

 very similar, but the growth of the two lobes of the cotyle- 

 dons is even more luxuriant, so that they actually overlap. 

 A structure more or less similar occurs in other genera of this 

 family. 



The emargination is very much deeper in other groups, 

 and due to other conditions, for instance in the Convolvulaceae. 

 In Convolvulus Soldanella (fig. 87) the embryo, which is 

 eventually very large, lies at first straight in the seed em- 

 bedded in a clear jelly-like endosperm, and rests on a solid 

 ovate, grooved, white ridge (fig. 87, B and C, a), which rises 

 from close to the micropyle. This tongue-like ridge grows 

 with the embryo. At the opposite end of the seed the raphe 

 and chalaza form a somewhat prominent ridge (b) projecting 

 into the endosperm. The cotyledons in this stage are plano- 

 convex, applied face to face, orbicular, entire, green, with 



