154: University of California Publications in Botany [Vol.6 



In this special case one might suppose that the epiphyte is adapted 

 to the same kind of locality as Postelsia, the exposed upper or even 

 supra-littoral rocks, where the surf is very constant and violent and 

 where Postelsia forms a pure or almost pure stand. If Saunders' 

 statement as to his plant also inhabiting "mussel-shells in the vicinity 

 of tufts of Postelsia" is right, it forms a support for our theory that 

 it is the nature of the locality more than an adaptation to life on 

 Postelsia that explains why the epiphyte does not occur on other algae 

 in other situations. 



The tufts of " Leptonema" are sometimes very dense, covering only 

 a very small area, sometimes, especially on the stems of the host, as- 

 suming tlie shape of somewhat larger patches of a short velvety indu- 

 ment. They consist of innumerable simple filaments, monosiphonous 

 while sterile (pi. 17). The basal part is formed by branching, densely 

 interwoven filaments, creeping on the surface of the host or pene- 

 trating between the cortical cells. How this penetration first takes 

 place I am not able to tell — whether the filaments are able to break 

 through the thick cuticle or whether, Avhat I think more probable, they 

 take advantage of small epidermal fissures or irregularities. It is 

 difficult, either by scratching off small tufts and dissecting them or 

 by cutting sections through the cortex of Postelsia, to get a clear view 

 of the basal parts. The creeping filaments seem to grow by apical 

 cells. Narrow, thick-w^alled hyphae penetrate deeper between the cor- 

 tical cells, but they remain intercellular, and we have no reason to 

 believe that the plant is a true parasite. On plate 18 sections with 

 various fragments of basal layers with erect filaments are figured, 

 growing quite superficially or in small cracks in the cortex. Figure 4 

 shows a piece scraped ofi^ and seen from the lower surface, the pros- 

 trate filaments being dotted. It has a strong resemblance to certain 

 Myrionema disks, which become more or less dissolved when growing 

 between paraphyses or assimilators of a host plant. The conditions 

 are different here, consequently I believe that the disk figured on 

 plate 18 belongs to the same species. I have seen long filaments 

 producing the characteristic sporangia grow up from similar disks. 

 However, though the dimensions of our "Leptonema" vary to a certain 

 extent, some of the disks that carry narrower filaments with shorter 

 basal cells may belong to another organism, possibly a Myrionema. 

 I did not, however, see any hairs or reproductive organs developed. 



In the system of erect filaments there is a distinct difference be- 

 tween long and short branches. Long branches come onlv from the 



