THE FUNGI 263 



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spermatia are very much smaller than any other form 

 of spore in the Uredinese, their average diameter being 

 about one two-hundredth of a millimetre. They are pro- 

 duced in great numbers and are accompanied by a 

 gelatinous substance which swells up when wetted, thus 

 pushing out the spermatia through the neck of the flask. 



The structure of the spermatum, which has a single 

 large nucleus, and little protoplasm, indicates, as Mr. 

 V. H. Blackman has shown, that it is of the nature of a 

 male cell, but in all cases investigated it is certainly func- 

 tionless. A rudimentary form of germination has even 

 been observed, the spermatia, when cultivated in sugar- 

 solution, budding like yeast cells. 



The true method of sexual reproduction in the Uredineiie 

 has recently been cleared up by Mr. Blackman. In the 

 aecidium of Phragmidium Rubi, for example, a very common 

 parasite on blackberry leaves, a nucleus passes from a vege- 

 tative cell into the fertile cell which gives rise to a chain 

 of ?ecidiospores. The paired nuclei, however, do not unite, 

 but the secidiospores, and the cells of the mycelium produced 

 from them, remain binucleate (as are also the uredospores) 

 until the teleutospore stage is reached. The teleutospores 

 are, at first, themselves binucleate, but while they are ma- 

 turing the two nuclei fuse into one. Thus the life-cycle 

 is divided into two phases, a binucleate phase from the 

 secidiospore to the teleutospore, and a uninucleate phase 

 from the latter to the secidium. Mr. Blackman regards the 

 pairing of nuclei in the aecidium stage, and not their fusion 

 in the teleutospore, as the true sexual act. Various modifi- 

 cations of the process have been met with in other Uredinese. 

 It appears, in all cases, to represent a reduced form of sexu- 

 ality, replacing the fertilisation by spermatia, which was 

 presumably the original process. Analogous phenomena 

 have been observed among some of the Ascomycetes. 



