86 ON SEEDLINGS 



tips of the cotyledons, which are rather broad and burst their 

 investments during germination. Those of Scabiosa australis 

 are linear-oblong, and do not burst the fruit and involucel 

 during germination (fig. 449), and if the latter are fairly well 

 covered with soil they are left in the ground when the embryo 

 makes its exit. The cotyledons ultimately become broadly 

 oblong and distinctly emarginate. The two primary leaves 

 are broadly oval, and shortly petiolate (fig. 450). The fruit 

 and involucel of this species closely resemble those of Dipsacus 

 ferox, and its different behaviour during germination is ac- 

 counted for by the fact that there is a small tooth-like pro- 

 jection on one side of the base of the hypocotyl (fig. 449, B), 

 and this, fixing itself in the small rim or lamina of the 

 involucel, holds it down while the cotyledons are drawn out. 



A second distinct type is represented by Scabiosa Gram- 

 untia (fig. 453). The involucel has a well- developed cup-like 

 lamina, and the radicle on germination pierces it, and holds it 

 firmly to the soil by means of a thickening at the base of the 

 hypocotyl while the latter on lengthening draws out the coty- 

 ledons. This thickening is symmetrical or equal all round, 

 not unilateral as in S. australis. The fruit of S. Columbaria 

 is rather thicker and shorter, while the cotyledons are also 

 shorter, but in no other respect do they or the germinating 

 seedling differ from S. Gramuntia. 



In the third type the radicle of the germinating seedling 

 pushes through the sides of the involucel, beneath the thick- 

 ened rim at the base of the lamina. The base of the hypocotyl 

 also has a symmetrical, annular thickening as in the second 

 group. The involucel of Scabiosa palaestina (fig. 451) is 

 salver-shaped and attains a much greater size than that of any 

 other species observed. The lamina is particularly large, 

 membranous and traversed by straight radiating nerves ex- 

 current at the margin, forming a deeply fringed border. 

 Beneath the thickened rim at the base of the lamina are 

 numerous perforations, through one of which the radicle finds 

 its way, fixing the fruit to the ground. The cotyledons 

 ultimately become obovate-spathulate and slightly emarginate. 

 S. graminifolia has likewise a perforated involucel. The 

 thickening of the hypocotyl is well shown by S. atropurpurea 



