206 



PROTOBASIDIOMYCETES 



[CH. 



in kind from the normal process. In Pinus sylvestris^ the male and female 

 nuclei lie side by side but do not fuse till their chromosomes become mingled 

 on the first spindle of the embryo ; in many of the protozoa and in some 

 other animals a series of conjugate divisions may precede the combination 

 of the paternal and maternal chromosomes in a single membrane. 



Fig. i8i. Puccinia Potiophylli S.; 

 fertile cell of teleutosorus giving 

 risetoteleutospores; after Christ- 



Fig. iS'Z. Phraamidium violaceum Went.; a. teleuto- 

 spores, X 1080; /;. fusion of nuclei in teleutospore, 

 X 1520; after Blackman. 



It may be hazarded that in the Uredinales the similarity of the physio- 

 logical history of the nuclei before they become associated is responsible 

 for a minimum of attraction between them, so that there is no sufficiently 

 strong impulse towards fusion till meiosis is about to take place ; being, 

 however, in the same cell, they have no opportunity of dissolving partnership 

 and the influences which bring about meiosis affect both alike. 



A considerable similarity exists in the arrangement of the different 

 groups of sporogenous cells. The uredo- and teleutosori are clearly com- 

 parable, both are of indefinite extent, with or without a border of paraphyses, 

 and both consist of groups of rectangular basal cells from which the spore 

 mother-cells arise in horizontal series and divide to produce the simple or 

 compound spore and the stalk-cell. Sometimes, however, the uredospores 

 are borne in vertical series, one below the other, and the sister-cells of the 

 spore form short, intercalary cells instead of stalk cells (fig. 183). 



This arrangement and that of the so-called primary uredospores link the 

 uredosorus to the aecidium, suggesting the homology of the stalk and inter- 

 calary cells. In the simplest aecidia, those of the caeoma type, we have a 



^ Blackman, V. H., 1898, Phil. Trans. B. cxc, p. 395 



