BELATION BETWEEN GONIDIA AND HTPH^ IN LICHENS 177 



the others give off branches where they come in contact with algal 

 cells and thus become closely connected with them. If the hypha^ 

 on leaving the promycelium are prevented from fulfilling their func- 

 tion, they die. Generally speaking, the expansion of the hyphal 

 filament into sepairate spherical distentions does not appear as any- 

 thing exceptional. 



Of especial interest in this connection are the descriptions of 

 Zukal, and then Fiinfstiick and Bachman's so-called spheroidal cells, 

 most often met with in lichens on a substratum of limestone (calci- 

 vores). These were considered first as reservoirs of stored material 

 and secondly as secretions. But if the spheroidal cells appear merely 

 as outgrowths, consisting of substances not required for the fungoid 

 organism, then perhaps the analogy between the distensions of intra- 

 gonidial hyphae I have described and the spherical cells is entirely 

 superficial : similarly, the analogy between the spherical shoots of the 

 germinating spores of Pertusaria communis etc. and between the 

 same spheroidal cells must also be superficial. This interesting ques- 

 tion demands further investigation. 



Let us now pass on to the second type of intragonidial hyphfe, 

 which differ from those described above by the obvious pi'esence of a 

 cell- wall. This type of intragonidial hypha is, as a matter of fact, 

 in no way distinguishable from the ordinary hyphal thread. This 

 class of intragonidial hypha was studied by Elenkin in Lecidea atro- 

 hrunnea. A very large number of gonidia, especially the largest, 

 appeared as if crammed with thick- walled hyph;© containing drops 

 of oil highly refractive in appearance. I have observed this type of 

 intragonidial hypha only in those gonidia which have lost all or nearly 

 all their protoplasm. Instead of the usual contents, in this case the 

 gonidia were filled with hyphae, which lay as a closely packed mass 

 inside the gonidial envelope. 



Having stated the facts observed, let us now endeavour to explain 

 their true significance, and to dedvice some conclusions as to the 

 reciprocal relations of the different parts of a lichen, taking care not 

 to lose sight of the fact that the following, like all deductions from 

 observations made, needs experimental proof for its complete justi- 

 fication. 



The direct contact of the hyphse with the cell-walls of living 

 gonidia makes possible an exchange by osmosis or food material 

 between the fungus and the alga. The extended network of the 

 hyphal cells around the gonidia and the enlargement of the surface 

 of contact by means of the formation of a club-shaped hyphal dis- 

 tention, which I have noted, would, without doubt, to a lai-ge extent 

 assist such an exchange ; but the entire absence in this case of 

 experimental proof of the possibility of osmosis through the hyphal 

 and gonidial envelopes forbids a definite conclusion on this point. It 

 will readily be granted that when two cells of different character 

 come into contact, they may be equally pervious, or one of them may 

 be semipervious, or, again, both may be semipervious in regard to the 

 same substances, or both semipeiwiovis, but in regard to different 

 substances, thereby creating a possibility of osmotic filtration of some 

 substances into the fungus and others into the alga. In short, the 

 JouBNAL OF Botany. — Vol. 56. [June, 1918.] n 



