20 BULLETIN 395. U. S. DEPAETMENT OF AGRICULTURE. 



RELATIONS OF MOISTURE. 



While no attempt was made to determine whether or not the 

 conidia will germinate in a highly humid atmosphere in the absence 

 of water, no evidence of this type of development was observed. On 

 the contrary, cumulative observational data strongly indicate that 

 at least a film of water is essential to germination. Continuous 

 wetting, however, is unnecessary, as was shown in the following 

 experiment: 



Experiment 1. — Spores were placed in drops of sterile distilled water and 1 per cent 

 prune decoction, respectively, on slides in moist chambers and incubated in diffuse 

 light in the laboratory at 15° to 25° C. In one series the drops were not allowed to 

 evaporate. In two others the spores were kept alternately wet and air dry for 24-hour 

 periods, one series being wet during the first period and the other dry. The experi- 

 ment was continued for six days and noted daily. The spores which were kept con- 

 tinuously moist germinated normally and at the end of the experiment showed some- 

 what better growth than the others. Those which were alternately wet and dry 

 showed littte if any injury from the treatment. They ceased to develop when dry, 

 and resumed their activities when wet. At the end of the experiment these two series 

 were indistinguishable in their development. Other similar tests in whi ch the periods 

 of wetting and drying were varied gave confirmatory results, no serious injury being 

 observed unless the changes were very frequent in the earlier stages of germination. 



RELATIONS OF TEMPERATURE. 



Several series of germination experiments were conducted in drops 

 of sterile distilled water and 1 per cent prune decoction, compara- 

 tively, on glass slides in moist chambers in darkness at carefully 

 controlled temperatures ranging from 2° to 35° C. The spores were 

 taken from vigorous Lima-bean agar cultures 2 to 4 weeks old. At 

 2° C. germination in sterile distilled water was practically nil, only 

 occasional tubes, with a maximal length of about 20 p., being observed 

 at the end of 15 days. In the parallel cultures in prune decoction, 

 early evidences of germination were visible after three days. Within 

 four days numerous tubes 5 to 10 ju long were evident, while at the 

 end of 15 days most of the spores had germinated, their tubes averag- 

 ing more than 100 ix in length. At 4° and 6° C, respectively, the rate 

 of development was slightly increased. At 9° and 12° C. it was in 

 each case materially accelerated, and up to 20° it increased steadily. 

 The cultures at 24° C. were slightly more advanced than at 20° and 

 almost indistinguishable from those at 27°, though apparently very 

 shghtly more vigorous. At 30° to 32° C. the spores germinated but 

 sparsely. The tubes in the prune decoction rarely exceeded 60 ix 

 in length and failed to develop into mycelia or -to produce spores. 

 At 35° C. no germination was observed. 



It appears, therefore, that the thermal relations of germination 

 closely parallel those of subsequent growth, the minimal tempera- 

 ture for germination in water or in favorable nutritive solutions 



