4° Smuts in their Relation to Exists. 



akeady called attention in mv work on " The Rusts of Australia," to the dis- 

 coveries of Blackman and Christman, showing that there are true sexual cell 

 fusions in the aecidial stage of the rusts, and this has been extended to forms 

 possessing uredospores and teleutospores by Olive^ and others. Dangeard^ 

 has also shown that when sexual reproduction, as he considers it, is about to 

 take place in the smuts, the cells concerned become swollen. Each single 

 swollen cell contains two nuclei, and the fusion of these two nuclei to form 

 one is regarded as an act of fertilization. But this is not the kind of fertiliza- 

 tion which occurs in the rusts investigated, and it will be necessary in order 

 to understand clearly the relation between the two. to give a brief life-history 

 of both. 



In the rusts the condition in which two nuclei occur in a cell is shown to 

 arise in aecidia in the fusion cells or " basal cells," so called because they 

 subsequently give rise to the chains of a^cidiospores. The binucleate basal 

 cell is the result of the conjugation of two uninucleate cells, so that the contents 

 of two distinct cells enter into its composition. The nucleus, together with 

 the protoplasm of one cell passes into the other cell by means of a pore in the 

 wall separating the two cells, and the latter or receptive cell is thereby 

 fertilized. These sexual cell fusions may either represent true sexual 

 reproduction, in which the two uniting cells are clearly distinct like the 

 ovum and sperm, or the two uniting cells may show no appreciable differences. 

 The former, is called by Winkler,' Amphimixis and the latter Pseudomixis, so 

 that we have here an instance of Pseudomixis, for the two fusing cells, as 

 well as their nuclei, are approximately equal. 



The myceUum which bears the uninucleate fusion cells has also single 

 nuclei, but the product of the fertilized cell is a growth with paired 

 nuclei. Hence all the constituent parts of the spore-bearing 

 generation or Sporophjte show in their cells the paired nuclei, including 

 the aecidiospore, the mycelium arising from them, the uredospores, 

 and teleutospores. When uredo- and teleutospores only occur, they originate 

 from similar fusion cells, and Olive has investigated a species possessing 

 only teleutospores, and found that the binucleate condition arises in the 

 basal cells, which give rise to teleutospores almost immediately. 



The mycelium in the host-plant, bearing the sexual cells or gametes 

 which are all uninucleate, constitutes the Gametophyte. There are thus two 

 distinct stages of the rust starting in each case from a single cell. The 

 fertile cell is the starting point of the spore-bearing generation or Sporophyte. 

 and the spore is the beginning of the sexual generation or Gametophyte, and 

 there is a regular alternation of the sexual Gametophyte and the asexual 

 Sporophyte. 



In the smuts, on the other hand, only the asexual generation is represented, 

 and the single spore corresponds generally to the teleutospore of the rusts. 

 The mycelium has two nuclei in each cell, at least when young. In certain 

 swollen cells the two nuclei already contained in the cell combine and fuse 

 to form one, and it is this nuclear fusion within the one cell which Dangeard 

 considers sexual reproduction. It may also be remarked that in the rusts the 

 two nuclei finally fuse in the teleutospore as it matures. But it is of the 

 essence of the sexual process that the nucleus passes from one cell, representing 

 the male, to the female receptive cell, and it is just here that the difference 

 lies between the origin of the spore in the rusts and the smuts. The binucleate 

 swollen cell wliich becomes the spore in the smuts is not connected in any 

 way with a sexual process, while the spore generation in the rusts is the result 

 of sexual cell fusion. 



The smut spore otherwise, generally resembles the rust teleutospore in the 

 product of its germination. It produces a 3-4: celled filament bearing conidia. 



