BOTANICAL SUBJECTS. 113 



leaves and the pinheaded glands on the tips of hairs may mean. 

 Dasija sarcocaulon* may give him a hint that compound hairs 

 were originally branches of primitive plants. Delesseria cris- 

 patula\ will give him some notion of the origin of wings on 

 certain stems and petioles, as also of the sori on the terminations 

 of veins in ferns, as well as of the carpels of higher plants, here 

 called sporophyls. Halimeda macroloba% may give him some idea 

 of the cmdous development of the stems of the Cactacese. Poly^ 

 siphonia rostrata^ might suggest to him how the glandular hairs, 

 which we find on so many plants, may have degenerated into their 

 present condition, from reproductive hairs. On land plants we 

 often find them mixed up with ordinary hairs, just as they are in 

 this Alga. 



Further on in Phacelocarpus complanatus\\ we begin to meet 

 with the evolution of a midrib and lobes or teeth, and reproductive 

 organs on the teeth. ^ 



In Cystophora monilifera** we see a distinct stem and 

 branches, and a fructification differentiated from the frond, but 

 nevertheless, a modification of it. We see similar proorress 

 towards the types of land plants in Cystophora Sonderi,]] and in 

 Caulerpa trifariaXX arid others, we have a distinct rhizome, with 

 branches in one direction and roots in another. 



In giving the foregoing examples there is no pretence of 

 showing development step by step, but only of giving examples 

 which show progress from simpler to more complicated seaweeds, 

 xind a transition from these to land ferns, &c. 



In these seaweeds we seem to be able to trace the gradual 

 evolution of rhizome, stem, leaf, branch, lobes of leaves, teeth, 

 hairs, midribs, veins, catkins or spikes of sexual organs, roots, &c. 

 We find that these seaweeds at first have no roots. They are 



* "Han-. Phyc. Austr.," v. 5, pi. 278. 

 t » ' ,, Pl- 268. 



: „ „ pl. 267. 



§ ,, » pl.242. 



II „ „ pl. 252. 



^ Compare with teeth of young rose leaves tipped with a gland and other 

 leaves. 



** " Harv. Phyc. Austr.," v. 5, pl. 245. 

 tt » » pl. 243. 



XX » » pl. 261. 



A p. 1724. H 



