206 REPRODUCTION 



possible : those who consider them to be sexual structures call them spermo- 

 gonia ; those who refuse to accept that view write of them as pycnidia. 



Tulasne, Nylander and others unhesitatingly accepted them as male 

 organs without any knowledge of the female cell or of any method of ferti- 

 lization. Stahl's discovery of the trichogyne seemed to settle the whole 

 question ; but though he had evidence of copulation between the spermatium 

 and the receptive cell or trichogyne he had no real record of any sexual 

 process. 



Many modern lichenologists reject the view that they are sexual; they 

 regard them as secondary organs of fructification analogous to the pycnidia 

 so abundant in the related groups of fungi. One would naturally expect 

 these pycnidia to reappear in lichens, and it might be considered somewhat 

 arbitrary to classify pycnidia in Sphaeropsideae as asexual reproductive 

 organs, and then to regard the very similar structures in lichens as sexual 

 spermogonia. It has also been pointed out that when undoubted pycnidia 

 do occur on the lichen thallus, as in Calicium, Strigula, Pelttgera, etc., they 

 in no way differ from structures regarded as spermogonia except in the size 

 of the pycnidiospores and, even among these, there are transition forms. 

 The different types of spermatia can be paralleled among the fungal pyc- 

 nidiospores and the same is also true as regards the sporophores generally. 

 Those described as arthrosterigmata by Nylander as endosporous by 

 Steiner were supposed to be peculiar to lichens; but recently Laubert 1 has 

 described a fungal pycnidium which grew on the trunk of an apple tree and 

 in which the spores are not borne on upright sporophores but are budded 

 off from the cells of the plectenchyma lining the pycnidium. It may be that 

 future research will discover other such instances, though that type of sporo- 

 phore is evidently of very rare occurrence among fungi. 



b. COMPARISON WITH FUNGI. The most obvious spermogonia among 

 fungi with which to compare those of lichens occur in the Uredineae where 

 they are associated with the life-cycle of a large number of rust species. 

 They are small flask-shaped structures very much like the simpler forms of 

 pycnidia and they produce innumerable spermatia which are budded off from 

 the tips of simple spermatiophores. The mature spermatium has a delicate 

 cell-wall and contains a thin layer of cytoplasm with a dense nucleus which 

 occupies almost the whole cavity, cytological characters which, as Blackman 2 

 has pointed out, are characteristic of male cells and are not found in any 

 asexual reproductive spores. If we accept Istvanffi's 8 description and figures 

 of the lichen spermatia as correct, their structure is wholly different: there 

 being a very small nucleus in the centre of the cell comparable in size with 

 those of the vegetative hyphae (Fig. 115). 



1 Laubert 1911. s Blackman 1904. s Istvanffi 1895. 



