BOT.-VOL. I.] PEIRCE-NATURE OF LICHENS. 221 



to be dividing internally (figs. 6 and 9). From such divi- 

 sions there result new gonidia, but it is not necessary to 

 infer, as some do, that the gonidia are thus only amiably 

 doing their part toward the growth and the permanence of 

 the lichen. On the contrary, as Hedlund (1895) describes 

 for Catillaria denigrata (Fr.) and C. frasina (Fr.), and 

 as I have just shown in the above, we have in both cases 

 merely the attempt on the part of the gonidia to divide in 

 such a way as to exclude the haustoria from as many of 

 the daughter-cells as possible. That the gonidia cannot be 

 benefited, but are evidently injured, by having haustoria 

 within them, I shall show subsequently (page 226) ; and if 

 the haustoria are injurious, is it not sensible to suppose that 

 the gonidia will try to get rid of them ? If they are harm- 

 less or beneficial why should there be frequent divisions 

 which inevitably result in the formation of daughter-cells 

 free from haustoria ? In a culture, the conditions in which 

 seem to be more favorable to the uninjured gonidia than to 

 the much broken and greatly injured hyphae, the gonidia 

 succeed in eliminating the haustoria and in freeing them- 

 selves from enclosing hyphae. Imbedded in the body of 

 the Hchen, surrounded on all sides by hyph«,the advantage 

 in the struggle is to the other side ; but the struggle and 

 the manner of it are the same. The gonidia in the Hchen 

 seek by division to escape the hyphae. Some do — these 

 flourish and grow large; most do not — these divide again 

 as soon as possible and so remain small. 



IV. The Relations of Gonidia and Hyph^ as 

 SHOWN BY Microtome Sections. 



So far as I know, very little use has been made of modern 

 cytological methods in the study of lichens. This is to be 

 regretted, for without recourse to these, the intimacy of 

 the relations of gonidia and hyphae must remain compara- 

 tively obscure. It has already been demonstrated that our 

 culture-methods are still so defective, and the growth of 

 the fungus-component of lichens is so distressingly slow, 



