212 ON SEEDLINGS 



although semiterete have plenty of room to develop laterally 

 and become broad. 



A very important deviation not only from the type repre- 

 sented by Cerastium arvense, but also from the Order generally, 

 occurs in Arenaria procumbens. The embryo is curved as 

 usual in the shape of a horse-shoe, but the cotyledons are 

 accumbent. The seed is reniform, very much compressed 

 laterally, with a distinct notch at the base, and a double coat, 

 finely reticulated on the surface. The cotyledons lie round 

 the periphery of the seed just within the endosperm, and in 

 the broader plane of the seed, yet they are semiterete and 

 very narrow. Perhaps the exceeding thinness of the seed, 

 which in transverse section is oblong with slightly indented 

 sides and ends, may account for this particular manner of 

 folding, although the narrowness of the cotyledons would 

 hardly justify the conclusion. Buffonia Oliveriana (fig. 202), 

 B. brachyphylla, and B. macrosperma agree with the above in 

 having accumbent cotyledons, but they differ slightly in the 

 form of the seeds, which are always few, generally two, in a 

 capsule. They are very deeply horseshoe-shaped, and verti- 

 tically, almost oblong or obovate. This unusual length is well 

 marked in B. Oliveriana and B. macrosperma ; and the latter 

 has comparatively thick seeds. The cotyledons are always 

 narrow and semiterete, or almost square in section in B. Olive- 

 riana, and equal the radicle in length. The embryo as a whole 

 is very much curved, almost encircling the whole of the greatest 

 circumference of the seed. 



A second most important variation occurs in some species 

 with distinctly winged seeds, standing in the same relation to 

 the reniform seeds with a curved embryo as Tunica pachygona 

 does to Dianthus with flat seeds and a straight embryo. 

 This type, which is very rare in the Order, is represented 

 by Spergularia marina. The seeds are suborbicular, very 

 much laterally flattened, and girt at the circumference by a 

 moderately wide wing which is slightly notched at the hilum. 

 In most cases winged seeds are adapted for dispersal by the 

 wind, but in the case of Spergularia it perhaps serves the 

 same object by enabling the seeds to float. The embryo is 

 curved as usual, peripheral, and similar in all respects to 



