BOTANICAL .-L'HJKC1>. 295 



Prickles ok Spine> : 



Tbes-e are described by autbors as liardeiied bairs, wbile spiiie.s 

 are said to be different-aborted brancbes, bardened stipules, petioles, 

 &c. I tliiiik tbe prickles on tbe margins of leaves, sucb as tbose 

 of Agave, Bromelia, and many otbers, are notbing bnt hardened 

 teetb, and tbese I bave sbown are notbing bnt lobes or abortive 

 brancbes. It will be sufficient to refer to tbe annexed Fig. 126 to 









^ c 



Fig. 126. Desmarestia liyulata, Lainour (*' Harvey's Phyc. Brit.," pi. 115) ; 

 («) teeth, (6) the same partially developed into "branches, (c) well 

 developed branches with marginal teeth. 



satisfy tbe reader tbat prickles on tbe margins of leaves are inter- 

 changeable A\-itb lobes or brancbes. I sball quote tbe author's words 

 regarding this alga, " All the pinnules are margined with minute 

 spines like teeth, which in young indi\iduals produce tufts of 

 delicate branching jointed fibres." 



Ptilota plumosa, Ag. (pi. 80, op. cit.), also shows very well tbe 

 change of teeth into branches. 



Reference mav be made also to Figs. 115 and 1 16 alreadv gi\cn 

 in discus.sing tbe teeth of leaves. 



In Desmarestia, all stages of de\ elopment can be seen from 

 prickles (the author calls them minute .«<pines) to brancbes. In 

 face of these facts, it ap}>ears to me tbat tbe distinction betwwn 

 prickles and spiufs has no longer any raison (Vftre, 



KeCAI'ITII.ATIUK. 



Atone end of tbe evolutionai-y ladder we admit that m11 cells are 

 both procreative and veget^itiv*', as Weismaun does. Al the other 

 end of tbe ladder a differentiation iov economical purposes takes 



