26 



spores in maintaining their existence. The heavy preponderance 

 of collections showing only urediniospores has long been recog- 

 nized as one of the prominent difficulties in the taxonomic study 

 of tropical rusts. 



But doubtless the most unexpected feature of the flora is the 

 large proportion of short cycle species. The opinions of Magnus 

 and Eduard Fischer have generally prevailed, that a shortened 

 life cycle is an indication of adaptation to a short season for 

 growth, and that such species are more numerous on high moun- 

 tains and far northward, where the brief growing seasons alternate 

 with long periods of cold. 



In the short cycle rusts the spores germinate for the most part 

 while attached to the host plant, and dissemination is by the 

 exceedingly small basidiospores, often called sporidia. The time 

 required for one set of basidiospores to infect a plant, mature the 

 fungus, and provide another crop of basidiospores averages from 

 one to two weeks. It looks like a provision for a hurry-up de- 

 velopment to escape extermination. But under a tropical sun in 

 the Greater Antilles we find that 25 per cent of the species are 

 short cycle forms. Evidently the explanation of this situation 

 is not the one usually given. 



Possibly the 65 per cent of species propagated by repeating 

 spores, and the 25 per cent of short cycle species, are the ex- 

 pression of tvvo ways the rusts have found to meet one and the 

 same set of conditions that menace their existence. It is likely 

 that some important problems in the elucidation of the very 

 complex development and behavior of the rusts, such as this one, 

 which have not been well worked out in temperate regions, may 

 be studied to advantage in the tropics. 



A more extended analysis of the West Indian rusts is scarcely 

 advisable, considering the limited knowledge regarding them. 

 To show how restricted our knowledge is it may be well to 

 recapitulate. Altogether 214 species are recorded at this time 

 for the West Indian islands. Of these 174 species are known to 

 occur in Porto Rico, which has an area of 3,500 square miles, 

 and only 136 species in Cuba, which is nearly thirteen times as 

 large, having 44,000 square miles. Jamaica with 5,000 square 



