RELATIONSHIP 23$ 



hyphae, as such, are absent. Eventually each ascogenous cell 

 becomes an ascus and forms 4 to 8 ascospores. 



Although the attachment of the spermatia to the trichogynes 

 has been observed in many species, the details of fertilization are 

 unknown. The cytological investigations of Faull (1911, 1912) 

 were unfortunately made upon two parthenogenetic species, La- 

 boitlbenia chaetophora and L. gyrwidanmi, in w^hich nuclear 

 fusion was observed to occur in the young ascus. Although 3 

 nuclear divisions give rise to 8 nuclei, 4 of these soon degenerate, 

 and the mature ascus contains 4 ascospores. 



The mature ascospore has 2 unequal cells; the larger is cov- 

 ered with a gelatinous material which attaches the spore to its 

 host. No conidia or other spore forms are to be found. A num- 

 ber of genera and species of the group are dioecious; in these 

 forms the ascospores are discharged in pairs and develop into 

 separate male and female plants growing close together on the 

 host. 



Relationship. The Laboulbeniales have been prominently 

 mentioned by those who support the red-algal theory of the 

 origin of the Ascomycetes. The presence of spermatia and 

 trichogynes and of sterile cells surrounding the procarp (archi- 

 carp) in both groups is certainly a striking instance of parallel 

 development, if nothing more. Furthermore, the protoplasts of 

 adjacent vegetative cells are frequently connected through pores. 

 Yet the difficulty of homologizing the asci with any structure in 

 the Rhodophyceae and the differences in chemical composition 

 of the cell ^^•alls in the two groups are strong arguments against 

 the supposed relationship. It is perhaps better to regard the 



Fig. 92. Various Laboulbeniales. A. Mature plant of Stigviatomyces baeri, 

 having both antheridial and ascogonial branches. The spermatia are being 

 shed and some are attached to the trichogyne. B. Two mature plants of 

 Amorphomyces falagriae, the one at the left ascogonial, at the right anthe- 

 rial. C. Ascus of Stigmatoinyces baeri. D. Ascospore of S. baeri, with 

 gelatinous envelope. E. Early development from the ascospore in which 

 foot-like attachment disk has formed. F. Young thallus of 5. baeri, with 

 foot, stalk cell (from basal cell of ascospore) and three vegetative cells 

 from upper cell of ascospore. G. Amorpboviyces africanus, illustrating 

 spermatial formation among the Ceratomycetaceae. H. Rhynchophoro- 

 Tnyces rostratiis, illustrating spermatial formation among the Laboul- 

 beniaceae. /. Stig7nato77iyces baeri, illustrating spermatial formation among 

 the Pevritschiellaceae. (Adapted from Thaxter.) 



