SIR J. I.TJBBOCK — PHrTOBIOLOOrCAL OBSEBTATIOXS. 



377 



'/^ 



Bistoj'ta *, &c Gray t observes tliat the economy of this urraiigc- 

 ment is not apparent. Assuming, however, that the elevation of 

 the cotyledons is an advantage, perhaps, as I have suggested, 

 from carryi]]g tlicm above the surrounding herbage, the combi- 

 nation of tlie two petioles — reversing tlie old fable of the bundle 

 of sticks— would, with the same amount of material, give a con- 

 siderable addition of strength. 



In other cases, however, the existence of j^etiolcs apparently 

 lias reference to tlie arrangement of the embryo in tlie seed. 



In the Geraniums, for instance, as has been already mentioned, 

 the cotyledons are folded on themselves, one half of each lying 

 t\'ithin the other. Fig. 91 represents an embryo partially un- 

 folded, and it will be seen that in the position assumed by the 

 cotyledons the petioles arc necessarily as long as half their breadth. 

 In Eucali/ptus Globulus, again (fig. 112), the mode of folding of 

 the cotyledons would be impossible but for the petioles. 



Fig, 94; 



Oerminatnig seedling or GerunUim bohrmicHm, X f>. 



Winkler, '*Ueber die Kcimblatter der deutschen Dicotjlen," Bmnacuburg 

 Bot, Ver. 1874. * ' Structural BoUuiy/ p, 21. 



