38 



ON SEEDLINGS 



ledons even within the limits of the same genus. For instance, 

 Delphinium Staphysagria (fig. 31) has the cotyledons sessile, 

 while those of D. elatum (fig. 30) have petioles. In Bryonia 

 laciniosa (fig. 75) the' cotyledons are nearly sessile, while those 

 of B. dioica (fig. 76) have petioles. 



There is nothing, so far as I know, in the structure of the 

 seed to account for this difference. It is observable, however, 

 that while the cotyledons of Bryonia laciniosa (fig. 75) and 

 those of D. Staphysagria (fig. 31) are raised by the hypocotyl 

 somewhat above the level of the ground, those of Bryonia 

 dioica (fig. 76) and of D. elatum (fig. 30) are attached close to 

 the ground. In fact the cotyledons are carried up in both cases, 

 but in B. laciniosa and D. Staphysagria 

 by the hypocotyledonary portion of 

 the axis or stalk of the plant, in B. 

 dioica and in D. elatum, on the other 

 hand, by their own petioles. 



I may also refer to Vitis hypoglauca 

 and V. cebennensis, the former with a 

 short hypocotyl and long petioles, the 

 latter with a long hypocotyl and short 

 petioles. 



In short, we may say that the coty- 

 ledons are, as a general rule, sessile 

 when they are raised by the growth of 

 the hypocotyl, while they are petiolate 

 when they take their origin close to the 

 ground. There are, no doubt, some exceptions ; for instance, 

 in some species of Hedysarum the cotyledons are radical and 

 yet sessile. I have, however, often in Algeria seen seedlings 

 of this group in hot exposed situations, where they ' held the 

 field ' alone, and being sure of ample heat and light did not 

 require to be raised above the surface. 



The opposite exception is perhaps more common i.e. 



when the cotyledons, though raised, are still petiolate. Here, 

 however, the cotyledons are probably petiolate for the same 

 reason as the leaves viz., when the foliage is large, leaf-stalks 

 are an advantage in carrying the lower leaves out of the 

 shadow of those immediately above them. 



FIG. 76. Seedling of 

 Bryonia dioica. Nat. size. 



