Weaver: effects of rusts upon tkansitratjon 381 



cases less than that of the healthy, and that the ratios were in gen- 

 eral the same at any given period of the day. They determined the 

 average ratio of transpiration for the diseased and healthy leaves 

 of the York Imperial to be 78.3 and for Ben Davis 74.2. 



An Analysis of the Project 



Stated briefly, the aims of the present investigation were : 



To determine whether or not rusts increase transpiration. 



To determine the relation between the increased transpiration 

 and the extent of the affected area. 



To determine the time of the beginning, and the rate of the in- 

 crease. 



To determine the behavior of rusted plants and controls, as re- 

 gards transpiration, under dift'erent environments. 



To determine these relations for several species of plants, chiefly 

 cereals, and for several kinds of rusts. 



These determinations were made by means of the following plant 

 materials : 



Plant parts of same age, size, thickness, etc. (example, isolated 

 opposite leaves). 



Plants of approximately constant transpiring area, kept thus by 

 clipping off new parts (example, wheat). 



Entire plants: (a) experimented with for short periods so that 

 increased growth would be small; (b) experimented with for longer 

 periods where growth would be approximately proportional, or 

 where the original and final transpiring areas were measured. 



Since the purpose of the investigation was to determine the re- 

 lation of water loss between diseased and healthy plants, extreme 

 precautions were taken to keep all of the environmental factors ex- 

 actly the same for both kinds of plants throughout an experiment. 

 The method varied somewhat, depending upon the kind of plant 

 used, but since most of the work was done with the smaller cereals, 

 a typical case may be given, departures from which will be noted 

 as other types of plants are discussed. 



The plants were grown in ordinary glass tumblers of about 250 

 cc. capacity. An ordinary sandy-loam potting soil was used. To 

 insure equal volume, water content, and aeration, the soil was 

 screened through a 2-mm. -meshed sieve, brought to good tilth, and 

 again screened through a 5-mm. -meshed sieve, after which it was 



