1886.] 



MICKOSCOPICAL JOURNAL. 



103 



compelling it to pay tribute. Indeed 

 Schvvendener himself was frank 

 enough to admit that we could not 

 settle this question by isolated, one- 

 sided observations, but only by care- 

 full}' conducted experiments in the 

 culture of lichen-spores, lichen-goni- 

 dia, and unicellular algae. Accord- 

 ingly many experiments in lichen 

 culture have been conducted since 

 the promulgation of the Schvvenden- 

 erian hypothesis, but in no instance 

 have they been satisfactory. In the 

 first place it was found exceedingl}- 

 difficult to imitate the conditions of 

 nature closely enough to allow more 

 than the first stages of growth to 

 progress. While the spores germi- 

 nated freely, they could not be car- 

 ried beyond a certain loosely cellular 

 stage which never exhibited the 

 slightest traces of gonidia nor pro- 

 duced perfect lichens. 



Another method of culture called 

 Synthesis has been attempted ; that is. 

 the manufacture of lichens by sowing 

 their spores upon certain alg^. Thus, 

 Rees sowed spores of Collema glau- 

 cescens upon Nostoc Hceiioides. Bor- 

 net sowed the spores of Physcia par- 

 ieti)ia upon Protococcus viridis. and 

 Treub sowed spores of Ramalhia 

 and Lanacora upon Cystococcus 

 humicola. These experiments, how- 

 ever, met with a very limited amount 

 of success, even where the spores 

 germinated and produced hyphae en- 

 veloping the algse. The process of 

 union was easily accomplished, but 

 instead of stimulating the algae to 

 greater activity, or producing new 

 lichen plants, the contact resulted in 

 the death of the algae, so that instead 

 of there ]:»eing an}- bond of sympathy 

 between them there exists a mortal 

 antagonism. 



■ But,' says Mr. Crombie, ' apart 

 altogether from such considerations 

 relating to lichen-culture, there are 

 two fatal objections to the hypothesis, 

 either of which is quite sufficient 

 f(jr its subversion. The first of these 

 has reference to the very peculiar 

 nature of the parasitism involved in 



the theory that the fungal hyphje are 

 nourished by the captive algals.' Par- 

 asitism of itself is of very common 

 occurrence in the vegetable kingdom, 

 but instead of stimulating the host to 

 greater activity, the contact is always 

 detrimental, and, if the parasite be in 

 sufficient force, is ultimateh' fatal. 

 But in the present case we have a 

 parasite exceeding by many hundred 

 times the size of the host, and yet, 

 instead of exhausting, it only stimu- 

 lates it to greater activity, a phenom- 

 enon which certainly occurs nowhere 

 else in nature. 



But, granting that this hj-pothesis 

 be true, ' Upon what,' Dr. Bentham 

 pertinently asks, ' do the gonidia 

 themselves feed ?' This is a very im- 

 portant point in the physiology of 

 lichens, ^yhich Schwendenerism does 

 not satisfactorily explain. Shut up 

 in a dark and narrow prison, and de- 

 prived of the free life they formerly 

 led by the tyrant who has enclosed 

 them in his meshes, they are cut off 

 from all communication with the 

 outer world, from which they could 

 receive such nourishment as they 

 themsehes require and the much 

 larger quantit\' their master extracts 

 from them. • Whence, then, and 

 how is this nourishment obtained ?' 

 Now, it is a well-established fact, 

 and one that no person attempts to 

 deny, that lichens obtain their whole 

 nourishment from water. It was 

 formerly supposed that they obtained 

 a portioh of their nourishment 

 through the rhizoides, from the sub- 

 stratum upon which they grow, but 

 this idea is now not accepted, the 

 rootlets merely serving to retain them 

 in position. 



Water, then, is the chief source of 

 their nourishment. This is poured 

 upon their surface and penetrates the 

 cortical layer to the vicinity of the 

 gonidia, which are the seat of special 

 vegetative activity. But the gonidia 

 are principally stimulating in their 

 effect, the real organs of nutrition 

 being the cortical layers. From this 

 it seems that neither the captive algae 



