Studies on Fungicides— II 19 



Those tables show, as do the preceding ones, that, when; two factors 

 are varied, as the optimum of the one is reached differences due to the 

 other tend to be minimized. Thus, for example, in the determination 

 of the optimum temperature it might be well to vary another factor also 

 in order that the temperature differences may be shown the more clearly. 



The optimum temperature for spore production may not necessarily 

 be the same as that for spore germination. An abundance of spores is 

 essential, and it may therefore be necessary to maintain the cultures at 

 a temperature for spore production which is different from that for 

 optimum spore germination. Limited tests here seem to indicate this 

 for conidia of Venturia inaequalis. 



Light 



None of the fungi tested exhibited any preferential light requirements. 

 This appears to agree with the results of most other investigators (Doran, 

 1922). 



Time 



Since the time limits for .the germination of spores vary greatly, it will 

 be necessary to determine this period for each fungus. If the test is dis- 

 continued too soon, not all the spores capable of germinating will have 

 done so; if the test is continued too long, the spores may have germinated 

 to such an extent as to form an indistinguishable tangle, not to speak of 

 the possibility of the drop's evaporating. Of course, in nature the 

 optimum conditions for germination may be present for such a short time 

 that but few spores may ever germinate successfully. In spite of this, 

 since fungicidal tests are chiefly comparative in character, it is advisable 

 to allow sufficient time for optimum germination. Doran (1922) has 

 compiled from the literature an interesting list of the lengths of time 

 required for representative fungus spores to germinate. 



APPLICATION OF THE FUNGICIDE 



It is very essential that care be exercised in the application of the fungi- 

 cide to the slides. For applying liquid fungicides a DeVilbiss atomizer, 

 " Atlas Spray No. 29," has been found very satisfactory and will deliver 

 the fine, uniform, mist-like spray desired. The dry fungicides, or dusts, 

 are applied by means of test-tube dusters, one of which is illustrated in 

 figure 1, a (page 11). These were devised by Dr. F. M. Blodgett, of this 

 laboratory, and have; long been in use here. .They are now widely em- 

 ployed in other laboratories as well (Lee and Martin, 1927:316). They 

 are very simple in construction, being made of a heavy-walled six-inch 

 test tube, a two-hole rubber stopper, two pieces of bent glass tubing, and 

 a rubber atomizer bulb. ( Hass tubing of 5 millimeters outside diameter 



