1893.] MlCiUJSCOPICAL JOl UNAL. 35 



nation takes place in water, whetlier in artificial culture or in a 

 drop of water on the surface of a leaf of the host-plant, the <^erm- 

 tubes are very slender, equal, simple, or sparint^ly branched, 

 spirally curved, transverse septa very rare, and the fusi(jn l)e- 

 tween ori'^inally distinct tubes or branches very rare, or in most 

 cases entirely absent (Figs. 4 and ^). About two days after 

 fjermination has commenced, one f>r more short lateral branches 

 sprin<^ at right angles from the germ-tubes : these may be con- 

 sidered as specialized sporo|)lu)res. 'I'he apex of each sporo- 

 phorc becomes slightly incrassaled, and within a day produces 

 several simple cjr branched concatenate chains of elliptical, pale 

 olive, smooth secondary spores. Tiiese secondarv spores are 

 developed in acropetal order (Fig. 4^'). 



When the spores germinate in a sterilized solution of the host- 

 plant {Stni/acina sfe/Zata), the germ-tubes measure ^^-6// in 

 diameter at the point of origin from the spore, become elongate, 

 never spirally twisted, and gradually taper to the apex ; trans- 

 verse septa are abundant ; the clusters of secf)ndarv spores are 

 about equal in uumlier, and the secondary spores of the same 

 size as those produced f)n the very slender germ-tubes formed bv 

 spores germinating in pure water (Fig. 3). In both instances 

 sporophores bearing clusters of secondary spores are not un-^ 

 frequentlv produced directlv by interstitial cells of the spore 

 without the intervention of a germ-tube (Fig. 3^ •- and Fig. 



Throughout the smnmer months the spores germinate as soon 

 as mature, at the ordinary temperature of the air ; but the later 

 batches of spores produced in September and October will not 

 germinate, or very feeblv, at the temperature of the air : such 

 spores remain passive during the winter, and germinate the 

 following spring. Nevertheless, these are not resting spores — 

 in the ordinary sense of the term — but will germinate at any 

 period throughout the winter, provided the temperature is 

 sufficiently high. 



During the summer the isolated patches of disease that corre- 

 spond to independent centres of infection increase in size and 

 run into each other, the whole leaf not unfrequently presenting 

 a blackened appearance, caused by the dark-colored hyphae. 



During the autumn the stronger branches of the vegetative 

 hvpha- increase considerably in thickness, manv of the cells be- 

 coming very much inflated and spherical and separated by deep 

 constrictions, due to the transverse septa not increasing in diame- 

 ter. Many of these stout hypha) become more or less irregularly 

 branched and contorted at the tip, the convolutions approach 

 each other, and iw repeated cell-formation produce a more or 

 less globose sclerotium-like body, almost black externally, some- 

 what paler inside (Fig. 11). These sclerotia remain passive dur- 

 ing the w inter. In the following spring certain of the external 

 cells of the sclerotia become more prominent than the rest, and 



