Host and Parasite in certain Diseases of Plants, 415 



Fig. 6. Diagram constructed to show the comparative effects of equal increments 

 of temperature on respiration and assimilation respectively, according to 

 Kreussler's data. The base line has marked off on. it a number of intervals 

 corresponding to so many degrees centigrade, as denoted by the figures ; on the 

 ordinates from these points are measured distances corresponding to Kreussler's 

 figures — numbers representing the comparative intensity of the functions in 

 question, if that at the lowest observed temperature is taken as unity. 



more light the plant can get, the better. There is evidence to show 

 that, as might be expected, light of great intensity concentrated by 

 means of a lens, &c, on to the assimilating apparatus, produces de- 

 structive pathological changes ; but we may also infer from everyday 

 experience with shade-plants {e.g., camellias) that the light may 

 be too intense for normal assimilation to go on,* and such is the 

 case. 



Another point of importance is the kind of light which reaches the 



factory mode of estimating " brightness," " intensity," " quantity," &c, of light 

 (see Sachs, ' Phys.,' pp. 301—302). 



* See Famintzin, 'Bull, de lAcademie de St. Petersbourg,' vol. 26, 1880, col. 296 — 

 314. Also Eeinke, ' Bot. Zeitg.,' 1883, No. 42, with literature. 



