112 Journal of A gricultural Research voi. xix. No. 3 



or rain water, and they probably furnish an expression of the conidia 

 dimensions and a means of comparison with other species which is as 

 accurate as it is possible to obtain. 



It is interesting to note that occasional monstrous conidia were seen, 

 resembling somewhat those described by Miyake {14) for Sderospora 

 sacchari. Since these have the same structure and history as those of 

 more usual size and appear to represent merely the upper extreme of the 

 widely varving conidia dimensions, they are regarded by the writer as 

 of no special significance. 



Germination of the fresh conidia takes place readily in dew, in rain 

 water, in water from clear brooks, in dilute nutrient solutions of various 

 kinds, and on similar solutions solidified with i per cent agar. When 

 once the conidia are dried, however, they will no longer germinate under 

 any conditions. On the moist surfaces of newly infected plants in the 

 field, large numbers of conidia may be found germinating vigorously at 

 any time from about 3 a. m. until dawn, but after the rapidly drying 

 effect of the early sun has been felt for one or two hours there can be 

 found on the same plants only shrivelled spores incapable of further 

 development. Germination is preceded by a swelling and consequent 

 alteration in size and shape of the conidium and invariably proceeds by 

 the protrusion of one or more germ tubes (Pi. 25, C-L). This may take 

 place from any part of the spore, and the hyphae thus produced may 

 simply elongate (PI. 25, C, J) or develop variously into extensively 

 branching systems (PI. 25, E, F, L). Occasionally the hyphae of germi- 

 nation grow up into the air for a short distance and produce at their tips 

 an ovoid swelling that might perhaps be interpreted as an abortive 

 attempt at a secondary conidium formation such as has been found in 

 other Peronosporaceae. In no case was the production of zoospores 

 by the conidia observed, although repeated attempts were made to 

 induce this method of germination. 



In spite of the ease with which the conidia produce germ tubes, all 

 attempts to induce continued independent development of the mycelium 

 in artificial media have been unsuccessful, the growth seemingly ceasing 

 when the nutriment of the spore is exhausted. In view of the tropical 

 habitat of this Sderospora it is of interest to note that the conidia ger- 

 minate readily when maintained at a temperature as low as 6.5° C, even 

 though the temperature at which they most commonly germinate is 

 from 20 to 24°. 



In spite of extensive search, none of the resting or resistant bodies 

 customarily encountered in this or other genera of the Peronosporaceae, 

 such as chlamydospores and parthenogenetic or normal oogonia, have 

 ever been found to be associated with the conidial stage of this fungus. 

 Every effort has been made to find such structures. The progress of 

 the disease has been observed in individual plants from the time of their 

 infection by the fungus to their ultimate disintegration in many varie- 



