462 



our vegetative plants, the splitting of cucumbers is most important. The 

 fruit suffered most of all, but sometimes the stems also cracked. Decreased 

 temperature, accompanied by continued rain, not infrequently causes the 

 total failure of harvests, since the cucumbers often show gummosis and are 

 attacked by various black fungi. 



Long, cool rain}^ periods also cause a j)remature leaf fall, badly devel- 

 oped heads in grain, a small amount of sugar and starch in beets, tubers, etc. 



Repeated showers have a very disastrous effect when they fall on 

 blossoming fruit trees and during the setting of the seeds of field crops. In 

 the first place, the insects, necessary for fertilization, cannot fly about so 

 freely, and secondly, the anthers will not open so well, nor will the pollen 

 grains stick so well on the stigma. 



Nevertheless, the theor}'- that the increase of bacteria and fungi is 

 always favored by periods of rain does not hold absolutely. Parasitic 

 diseases usually increase only if tiie rain is accompanied by warmth. On 

 the other hand, cold wet weather retards the growth of the most important 

 parasites (rusts, false mildew, etc.). 



In tropical regions, however, rain storms usually favor the development 

 of fungous diseases and, to give at least one example, we will mention 

 Busse's observations^ He found that the Phytophthora decay on the cocoa 

 fruits was especialy marked in rainy years. The amount of rain is not 

 decisive but rather the character of the storm. Mighty gusts of rain seem 

 to keep the fungus spores from settling on the smooth-shelled fruit ; but the 

 softer, more frequent rains, easily producing stagnant moisture in the de- 

 pressions in tlie soil and in the regions w^here the drainage is poor, have 

 proved favorable for the fungi. Those regions suffer less to which the fresh 

 sea breezes or some wind has unhindered access. 



Among cultivated plants in rainy seasons, the wind is a helpful agent 

 in the struggle against parasites. This helpful agent has never been suffi- 

 ciently credited for its work. The tops of trees should be freed of excessive 

 water by frequent shaking. This should be done especially in closely planted 

 orchards and in warm rainy periods. 



1 Busse, W., Reisebericht der pflanzenpatholog-ischen Expedition d. kolonial- 

 wirtschaftl. Komitees nach Westafrika. Tropenpflanzer 1905, p. 25. 



