1893.] MICROSCOnCAL JOURNAL. 247 



plasm, and this is granular and vacuolated but it is not divided 

 by cross walls. The protoplasm however is thought to contain 

 a large number of nuclei as if cell-division had taken place in 

 part. 



There is a process which takes place occasionally in Mucor. 

 It is called conjugation. A filament of the mycelium, when 

 growing in a moist medium, sometimes meets a second filament 

 of the same or a different i)lant, of course of the same kind. 

 When this happens the two filaments unite and a swelling takes 

 place at the junction. A cell wall then cuts off the end of each 

 filament, and the two cells thus formed fuse to form one cell. 

 This product of the fusion of the two cells is called a "zygote" 

 (Fig. 14). It has the same power as a spore, that is to say, it is 

 a starting point from which a new plant can be formed. This 

 process of conjugation is the equivalent of the process of "sex- 

 ual" reproduction in the higher plants. Its precise meaning in 

 Mucor cannot be stated except hypothetically. It is not cer- 

 tain that the process of conjugation occurs in Penicillium but 

 it is , t)n analogy of the cases of other fungi, highly probable. 



If the methods of study described for Penicillium be used for 

 Mucor, the hyphse are found to be filled with granular, some- 

 what vacuolated protoplasm. This is shown in Fig. 11. The 

 young sporangia can also be examined. They are, as shown in 

 Figs. 12 and 13, filled in an early stage with protoplasm not yet 

 differentiated into spores. The young hyph?e absorb iodine 

 with immense eagerness and are good subjects for the practise 

 of the staining method. 



3. — Cystopus candidus ; or V^hite Rust. 



This, in mature state, is a white scale on the surface of stems 

 and leaves of the water-cress, shepherd's purse and other cruci- 

 ferous plants. The thin papery scales cover the conidia which lie 

 below them on the summits of the hyphse. Both the^ forms of 

 moulds already studied are nourished on dead animal or plant 

 bodies. In the case of Cystopus, however, we have to do with 

 a true parasite. The mycelium of this plant lives in the inter- 

 cellular spaces of the living cress. We can get a good idea of 

 the plant by following the course of its development. A spore 

 floating in the air must fall on the stoma of a leaf or young por- 

 tion of the stem. Here it germinates, throwing out its young 

 hypha which grows into the host plant and there spreads out 



