40 ON SEEDLINGS 



connate into one terete piece for 55-75 mm. of their length, 

 split a little way at the base to allow the plumule to emerge, 

 free in the upper part, semiterete and slightly channelled 

 above. 



In this case it is obvious that if the petioles had been 

 separate, they would have been far too weak to stand upright, 

 and their length therefore would have been comparatively 

 useless. 



In Polygonum polystachyum, again, the petioles are con- 

 nate and form a hollow tube through which the leaves pass ; so 

 that the seedling has the appearance of possessing an erect 

 hypocotyl with nearly sessile cotyledons. 



In other cases, however, the existence of petioles appa- 

 rently has reference to the arrangement of the embryo in the 



In the Geraniums, for instance, as has been already men- 

 tioned, the cotyledons are folded on themselves, one half of 

 each lying within the other. Fig. 78 represents an embryo 

 partially unfolded, and it will be seen that in the position 

 assumed by the cotyledons the petioles are necessarily as long 

 as half their breadth. In Eucalyptus Globulus, again (fig. 90), 

 the mode of folding of the cotyledons would be impossible but 

 for the petioles. 



Lastly, in cases where the cotyledons do not leave the seed, 

 the petioles leave room for the free growth of the plumule, 

 as in Sapindus (fig. 43). 



LOBED COTYLEDONS. 



The great majority of cotyledons are entire, but some are 

 more or less lobed. For instance, those of the Mallow (fig. 35) 

 are broadly ovate, minutely emarginate, cordate at the base, 

 and three-lobed or -angled towards the apex, with three veins, 

 each running into one of the lobes. 



Those of Lavatera and Althaea are similar. The embryo 

 is green, curved, and occupies a great part of the seed. The 

 cotyledons are applied face to face ; then, as growth continues, 

 the tip becomes curved, and depressed into a median longitu- 

 dinal furrow, the fold of the one lying in that of the other. 



