674 Journal of Agricultural Research vol. xx, no. 9 



philippinensis. As in the case of the latter species also, germination 

 is invariably by the protrusion of one or more germ tubes (PI. 79, I, 

 J, K). 



In size, the conidia of the Visayan Sclerospora are very variable. 

 With respect to such widely varying bodies as the spores of this and 

 other genera of Peronosporaceae, recent investigations have shown that 

 it is no longer possible to delimit a species adequately by the extremes 

 or averages of a few measurements. Rather, there is required the 

 assembling and presentation in tables and graphs of a sufficiently large 

 number of representative measurements to give a quantitative as well 

 as a qualitative expression of the conidial characteristics of the species. 



Accordingly, in order to obtain data adequate to identify the Visayan 

 form and to furnish a basis for comparing it with others, 700 conidial 

 measurements were made. These comprised measurement groups of 

 100 conidia from each of the two sugar-cane and the four Saccharum 

 spontaneum plants from Cebu, and from one maize plant inoculated 

 from the latter. 



The conidia were taken from the leaves of the host at night during 

 the optimum period of conidia production — from 2 to 4 a. m. — mounted 

 in dew, and measured immediately. 



Since, on examination, the seven measurement groups were found to 

 agree in all essential particulars, they were combined into the total of 

 700. For the purposes of comparison, 700 measurements of Sclerospora 

 philippinensis were secured in like manner. 1 Of these, 300 were new 

 ones made of fresh conidia from teosinte and sorghum found infected in 

 the college plots and from Saccharum spontaneum seedlings artificially 

 inoculated from maize. All these groups were compared, found to agree, 

 and grouped into the total of 700. 



In making these measurements, care was taken to include every 

 conidium in a marked area of the microscope field as the slide was moved 

 along by the mechanical stage. Only those conidia obviously injured or 

 those still attached to the conidiophores were excluded. The divisions 

 of the eyepiece equaled approximately 1.8 ll, and, with the magnification 

 used, it was possible to estimate with fair accuracy to one-third of a 

 division, or to about 0.6 fx. Consequently, the measurements are exact 

 to this extent — that is, the conidium recorded as 32 ll in length may as 

 well be 31 .4 ll or 32.6 ll instead of exactly 32 fx but not, in all probability, 

 3 1 or 33 fx. With a large number of spores such differences tend to equalize 

 themselves. As a result, the measurements presented here may be 

 considered as adequately representing the characteristics of the conidia 

 of the species involved. 



1 The writer wishes to take this opportunity to call attention to an error in the tabulation of the previous 

 spore measures of Sclerospora philippinensis (12, p. no). In the table of length, the conidia measuring 41 

 to 42.9 m should be 23 in number instead of 24. 



