140 



large quantity of large, ovoid or globular, colorless cells 

 filled with water. 



In Rosa berberifolia the pétiole bas esseiUially the 

 same structure as that just described; the same ihree fibre- 

 vascular bundles, but mueh less ground tissue, mucb 

 more sclerencbyma and, few or, none of the watercells. 

 1 présume therefore, that the stipules in R. berberifolia 

 are suppressed, but that potentially they are présent and 

 possibly under culiivation as the plant acquires vigor fully 

 developed stipules may be formed. 



The aculei are purely epidermal structures and by no 

 means siipulary though it is true they often occupy the 

 position of stipules. 



Development of the leaf. — An examination of the deve- 

 lopment of the leaf shows that it begins as a pimple (or 

 mamelon) whieh grows from below upwards and more so 

 on one side than on the other, so that at a very early 

 stage, the domeshaped pimple is replaeed by a hood open 

 on one side and forming a cavity in whieh the nexl 

 youngest leaf is partially coneealed. The development is 

 therefore quite that of an ordinary Rose-Ieaf except that 

 the latéral pinnae are not developed, though potentially 

 they are so, hence we may expect to see Rosa berberi- 

 folia some day produce, by accident, a true pinnaie leaf. 

 Some plants whieh ordinarily produce pinnale leaves, 

 occasionally develop unifoliolate leaves only, ihus, for 

 instance, there are in culiivation unifoliolate varieties of 

 Ash {Fraxinus), Strawberry (Fragaria), Gleditschia, etc. 

 Pubescence. — The vestiture varies considerably in 

 différent spécimens some being almost entirely glabrous* 

 others puberulous. The dentation of the leaves is similarly 

 variable. 



