222 CLASS ASCOMYCETEAE 



there in the interior of the colony. The ascogonia are similar to those in 

 Collema but the trichogynes are longer and do not extend to the surface. 

 They are attracted, apparently chemotropically, to the clusters of sperm 

 cells and grow toward them, coiling around and uniting with them. The 

 subsequent development is identical with that in Collema. (Fig. 73C.) 



In a number of other genera (e.g., Physcia) spermogonia and tricho- 

 gynes are produced. The former are various in shape, spherical or de- 

 pressed globose or lobed and immersed (except for the ostiole) or partly 

 or almost completely emergent. The sperm cells (spermatia) are minute, 

 one-celled, and usually slender, rarely rounded. They are produced 

 apparently successively at the apices of unbranched antheridial hyphae 

 or on the upper portion of the cells of the multicellular simple or branched 

 hyphae. They were studied in great detail by Lindsay (1861, 1872) in 

 many genera of lichens from all parts of the world. Adherence of sperms 

 to trichogynes has been observed but rarely. In a few cases an opening 

 has been observed between sperm and trichogyne but nuclear passage 

 has not been seen. Probably the sperm is functional in most cases of this 

 sort. In those species in which ascogonia have been reported but no 

 spermogonia are known the structure reported above for Collemodes 

 should be sought for before denying any type of sexual union. In many 

 lichens the ascogonium produces no trichogyne and may even be but a 

 straight row of a few cells. In one or two such cases adjacent cells of the 

 ascogonium lose their intervening septa whereupon ascogenous hyphae 

 begin to appear. Just what the nuclei do in that case can only be sur- 

 mised. Sexuality seems to be on the decline in this order as throughout the 

 Higher Fungi. The Moreaus (1926, 1928) have studied the reproduction 

 of many lichens and deny any sexual function to the spermatia, consider- 

 ing them when present to be modified conidia. (Fig. 74.) 



Because of the possession of a functional trichogyne and the produc- 

 tion of separate sperm cells and of asci a certain degree of relationship 

 between the Lecanorales and Laboulbeniales can be postulated, but they 

 are certainly widely divergent from any common ancestor. This may 

 have been an alga somewhat like some of the filamentous, freshwater 

 Florideae. It would require the assumption that subsequent to the acqui- 

 sition of the ascus-producing habit the one series developed as parasites 

 on insects with little modification of the protected procarp while the other 

 series developed as parasites on algae, presumably at first submerged 

 forms, later land algae. At the same time the spore fruit deviated far 

 from the simpler procarp typo shown in the Laboulbeniales. Here again 

 it must be noted that many mycologists hold that the sperm cells are 

 nothing but modified conidia which have taken up secondarily the sexual 

 function in place of an antherid. The external similarity between these 

 groups and the Flcjrideae would be looked upon from this viewpoint as a 

 case of convergence, not as an indication of true phylogenetic relationship. 



