THALLOPHYTA 451 



the upper cell an appendage is developed bearing a number of unicellular, flask- 

 shaped antheridia (D, an) from which naked spherical spermatia without cilia are 

 shed. The lower cell divides into four (D, a, b, c, d\ and the cell a projects and 

 gives rise to the multicellular female organ. The true egg-cell (E, ac], which is 

 called the carpogonium, is surrounded by a layer of cells. Above the carpogonium 

 come two cells (E, tp, t), the upper of which is the freely-projecting trichogyne or 

 receptive organ for the spermatia. After fertilisation the carpogonium becomes 

 divided into three cells, of which the uppermost disappears, the lowest (F, $t) 

 remains sterile, while from the middle cell the asci grow out. Each ascus (G) 

 produces four spindle-shaped, bicellular spores. The sexual nuclei become associated 

 in a pair in the carpogonium and divide conjugately. The nuclear fusion only 

 takes place in the young ascus. In certain species in which antheridia are wanting 

 a second nucleus, according to FAULL, is derived from the stalk -cell of the 

 trichogyne. 



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Sub-Class II. Basidiomyeetes ( l > 51 > 52 > 75 ^) 



The Basidiomyeetes no longer possess sexual organs ; only in 

 the Uredineae or Rust Fungi are structures found which can be 

 regarded as persisting, though functionless, male organs, and cells 

 which appear to correspond to the carpogonia of Ascomycetes. In 

 place of asci, BASIDIA are present which produce by a process of 

 budding in most cases four BASIDIOSPORES. The basidia agree with 

 the asci in containing when young two nuclei, which fuse with one 

 another. The reduction division appears to follow on this nuclear 

 fusion or karyogamy. The resulting nucleus undergoes two 

 divisions, and the four resulting nuclei pass into the spores which 

 are budded off (Fig. 397). 



The alternation of generations present in the Ascomycetes can no longer be 

 demonstrated in the Basidiomyeetes (with the exception of the Uredineae) owing 

 to the absence of the sexual organs. The union of sexual cells is replaced by 

 cell-fusions that result in binucleate cells. The pairs of nuclei correspond to 

 diploid nuclei, but fusion of the two haploid nuclei of the pair only takes place 

 in the young basidium. On the division of the truly diploid nucleus thus 

 produced, haploid nuclei again arise. 



The basidia present three distinct types. In the orders Uredineae 

 and Auricularieae the upper portion of the basidium is divided by 

 transverse walls into four cells ; each cell bears a single spore on 

 a thin stalk (sterigma), arising near the upper end (Figs. 403, 408). 

 In the Tremellineae, on the other hand, the basidium is divided by 

 longitudinal walls into four cells, each of which continues into a 

 long tubular sterigma (Fig. 398). The basidium in the Exobasidiineae, 

 Hymenomycetes, and Gasteromycetes is unicellular, and bears as a 

 rule four spores at the summit ; these may be sessile or situated on 

 sterigmata (Figs. 397 ; 420, 2). The Ustilagineae are of interest, since 

 in one family of these fungi the basidia are divided, while in the 

 other they are undivided ; the number of spores produced is not a 

 definite one, but often very large. 



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