046 STATE BOARD OF AGRICULTURE. 



Relation to Various Factors: 



Desiccation : 



Exuding spore masses from a pure culture, in which spore masses had 

 just appeared were transferred to 15 sterile cover slips in a Petri dish. 

 A spore suspension was made from spores from the same culture and a 

 drop of it was placed on each of 15 other sterile cover glasses. These 

 were kept in a sterile Petri dish when dry. After varying lengths of 

 time (see table) these slips were lifted with a sterile forceps and plant- 

 ed in tubes to tomato agar. The results were as follows: ( + ) indicat- 

 ing growth; ( — ) no growth. 



TABLE 2.— EFFECT OF DESICCATION: TEST WITH SPORE MASSES AND SPORE 



SUSPENSION. 



Started 9-11-14. 1 Started 9-14-14. 



Spore Masses. [ Spore Suspension. 



9-11-14 9 P. M. -f 1 9-14-14 10 A. M. 4- 



9-12-14 9 P. M. -{- I 9-15-14 10 A. M. + 



9-14-14 10 A. M. -f ' 9-16-14 10 A. M. + (?) 



9-15-14 10 A. M. + 9-17-14 10 A. M. + 



9-16-14 10 A. M. - 9-18-14 10 A. M. - 



9-17-14 10 A. M. - 9-19-14 10 A. M. - 



9-18-14 10 A. M. - , 



9-19-14 10 A. M. - I 



This experiment determined the resistance to drying as well as the 

 lack of influence of the matrix upon this resistance. This experiment 

 shows that the spore, whether in mass in the mucilaginous matrix or 

 isolated will not resist drying more than four days. The practical appli- 

 cation of this experiment is obvious. 



Heat: 



As was indicated (Page 17) an entire set of cultures on various 

 media were incubated at 371/2° forty-eight hours after inoculation at 

 room temperature (23°). These failed to develop. Furthermore, after 

 taking these out, fifteen days later, and allowing them to remain at 

 room temperature for four weeks, no sign of growth was evident. 



This was verified by inoculating 10 tubes of tomato agar; five were 

 placed in 371/2 ° C. incubator, five were retained at room temperature 

 (about 23° CO. The tubes which were incubated at 371/2° C. failed 

 to develop, while the check tubes developed normally. The tubes were 

 removed after 5 days and kept at room temperature but did not revive 

 after being kept one month at 23°. 



Observations in the field and of material sent in from various sources, 

 indicated a peculiar range in the size of spots. Pycnidia were present 

 but the actual spot formed varied greatly. Some leaves would show 

 numerous small spots separate and distinct from one another, covering 

 the entire leaf. On some leaflets the disease was manifested as one large 

 spot. These variations might be dismissed as due to weather conditions. 

 But, if it is possible under ordinary weather conditions to find spots of 

 pin-head size, may it not be that there are some weather conditions which 

 entirely inhibit the development of the organism? That this hypothesis 

 is tenable has been demonstrated by experimental evidence. Inocu- 

 lated tubes of cornmeal agar were allowed to develop for 48 hours and 

 were them placed in an incubator at 29°. These did not grow further in 

 the incubator. However, when taken out to room temperature these re- 



