1923] 



LEHMAN — POD AND STEM BLIGHT OF SOYBEAN 151 



48 hours. Germ tubes formed on the surface remain long, slender, 

 and sparsely septate. When germination of spores immersed 

 in the water occurs, the germ tubes soon develop septa and the 

 cells swell and branch in an irregular manner. In addition to 

 such requisites as proper temperature and moisture, there are 

 certain other factors which profoundly influence germination. 

 Much irregularity was at first experienced in attempts to ger- 

 minate pycnospores. A test on one day might yield fairly high 

 germination, whereas on the next day spores from the same 

 culture might entirely fail to germinate. Spores from one 

 strain might germinate well, while those from another strain of 

 the same age and grown on the same substratum might fail to 

 grow. Much of this irregularity was due in all probability to the 

 use of too heavy spore suspensions in the germination tests. It 

 has been repeatedly observed that the number of spores present 

 in a given quantity of water has a marked influence on the per- 

 centage of germination. This fact was demonstrated in the 

 following way: At maturity of the pycnidium, the pycnospores 

 exude through the ostiole and cling to the tip of the beak as a 

 small milky-colored droplet which can readily be removed by 

 use of an inoculating needle. Single drops of tap water on 

 depression slides were inoculated by placing one spore droplet 

 in each drop of water. Drops of tap water on a second slide 

 were inoculated by dipping a needle into the spore suspension 

 on the first slide and then washing it off in the water drops on 

 the second slide. The number of spores in the drops of the second 

 slide was always greatly less than that in the drops on the first. 

 These slides were kept in a moist chamber during the period of 

 the test. In all such trials germination in the drops with the large 

 number of spores was usually less than 1 per cent and never 

 above 2 per cent, while, in the drops with the small number of 

 spores, the percentage of germination seldom fell below 25, and 

 occasionally exceeded 75. The nature of the inhibiting factor 

 which prevents germination when an excessive number of spores 

 are present has not been determined. It may be due to inhibition 

 by some substance formed in the pycnidium while the spores are 

 developing, and in that event dilution should operate to increase 

 germination. That lack of free oxygen may be the inhibiting 



