100 ON SEEDLINGS 



The species of Helianthus and perhaps some other of their 

 allies may constitute another group characterised by their 

 large seeds and oblong-obovate, obtusely tetragonal fruits 

 which in transverse section appear of rhomboid outline. The 

 cotyledons of Helianthus annuus are broadly oblong, plano- 

 convex, and entire, and suddenly narrowed into a short 

 radicle. Those of H. cucumerifolius differ in their much 

 smaller size, and in being slightly emarginate, sometimes owing 

 to a depression at the apex of the achene. 



The species of Coreopsis are notable for their short, flat- 

 tened, winged or variously but unequally thickened fruits. 

 The winged condition is well shown in Coreopsis auriculata 

 (fig. 462), the fruits of which are obovate or, with the wings, 

 often suborbicular. The latter sometimes form a continuous 

 border to the lateral margins of the achene, but more often 

 are interrupted or broken in various places. The embryo 

 is broadly oval with a very short radicle. The fruit of 

 C. Atkinsoniana (fig. 460) is similar in outline, but the 

 wings are absent, and instead of being biconvex it is con- 

 cavo-convex owing to the inrolling of the thickened margin. 

 The embryo is somewhat curved longitudinally, and has 

 short roundly obovate cotyledons. C. filifolia (fig. 463) 

 differs markedly from either, in the seed being subcylindrical, 

 and slightly compressed, with the fruit greatly thickened 

 on the dorsal surface by means of cortical outgrowths 

 or blunt protuberances. The embryo is curved with linear 

 cotyledons. 



The relative size, shape, and number of fruits on a recep- 

 tacle have all a direct bearing upon one another. 



For instance, if the receptacle is narrow and flat it will 

 bear but a few fruits, or if they happen to be numerous then 

 a large number of them fail to reach maturity. This is well 

 shown in C. filifolia, which has from sixty-five to seventy-six 

 fruits on a narrow flat receptacle. Few of them reach 

 maturity, and those are narrow, as may be seen by reference 

 to fig. 463. 



On the other hand, C. auriculata bears from seventy to 

 one hundred and ten fruits on a receptacle which is broader 

 than in C. filifolia and elevated into a distinct torus, The fruits 



