BARBERRIES. 



607 



fell to the lot of the last-formed or uppermost leaves of the set. 

 As need arose for better protection of the infant shoots, the sim- 

 plest way of meeting it would be to increase the efficiency of the 

 parts already in use by widening them as far as might be neces- 

 sary. As this was going on, the same fate which overtook the 

 lateral leaflets of the original three would now extend to the ter- 

 minal one of each of these upper leaves ; for with the shortening 

 of the stem they would be brought to lie so closely above the 

 others as to shade them injuriously if not reduced in size. More- 

 over, as being the latest to develop, they would get but a small 

 share of the reserve food provided for the rosette. Still, their rela- 

 tion to the supply of nutriment as well as their uselessness or 

 power for harm in the rosette would, after all, be more a matter of 

 degree than in the case of the lateral leaflets, since these latter 

 would have to lie practically in one plane and so must interfere 

 not only with the terminal leaflets but with each other. This may 

 help us to explain why, although the lateral leaflets have so en- 



FIG. 11. BEKBERIS VULGAKIS. Series of spiny leaves passing into spines. 



tirely disappeared, we still find on some of the lower bud scales 

 traces of a blade which thus afford connecting links in our mor- 

 phological chain (Fig. 12). 



This evolution of the bud scales must, of course, have been 

 closely connected with that shortening of the petiole which we 

 have already noticed in the typical rosette leaves as having cul- 

 minated in the production of persistent overlapping scales forming 

 an outer bark for the secondary branches ; and it would seem most 

 probable that the development of bud scales and bark scales pro- 

 ceeded side by side. Finally, as accounting further for their sim- 

 ilarity of form, it may be remarked that in both, the protective 

 function, at first merely incidental to that of mechanical support, 

 comes at length to be the sole use for which they are retained : in 

 one case it is a matter of years, in the other of generations. 



