EXPERIMENT STATION BULLETINS. 591 



Under normal conditions on the host the organism is not subjected to strong 

 hght when it grows around the base of the plants just beneath the surface 

 of the soil. Long continued growth under such conditions may have pro- 

 duced a physiological adaptation to environmental conditions. At any 

 rate it is a significant fact that the light relations which are most favor- 

 able for development in culture are those to which the fungus is subjected 

 when functioning as a pathogenic organism. 



« 



EELATION TO DESICCATION. 



Mycelium of this organism will live for a period of two or three months 

 when grown on an artificial medium and allowed to dry. Longevity varies 

 with the character of the growth on the different media; rice, which pro- 

 duces thick tough mats of gro-wth and hyphae with thick walled cells, is 

 conducive to great resistance; soil and certain sjmthetic media produce a more 

 dehcate type of growth which succumbs more readily to desiccation. The 

 organism was grown on sterile muck until the soil was thoroughly filled with 

 a loose growth of mycelium. Samples of this were removed, placed in sterile 

 filter paper and subjected to drying at room temperature Plating brought 

 out the fact that the mycelium under these conditions was not living at the 

 end of 35 days but was still capable of producing growth at the end of 28 

 days. 



With many organisms, it is unquestionably true that longevily of spores 

 subjected to drying on glass surfaces furnishes no reliable index a» to their 

 persistence in nature. The longevity of fungus spores as well as of bacteria 

 depends largely on the medium upon which they are subjected to drying 

 and also on whether or not they are imbedded in a gelatinous matrix. 



Spores of Phoma apiicola were tested in the usual manner by drjdng them 

 on cover glasses and then testing their viability by placing them in broth. 

 Under these conditions 60 hours was the longest period that spores with- 

 stood desiccation. Other methods have been employed to more nearly 

 approach some of the conditions to which spores might be subjected in nature. 

 Celery seeds were treated with mercuric bichloride, thoroughly washed, 

 inoculated wdth spores and subjected to drying on sterile filter paper. The 

 seeds were placed in broth at regular intervals. Spores germinated after 38 

 days desiccation; above this, the limit of resistance seemed to be reached 

 and no more germination was obtained. To eliminate any inhibiting or 

 germicidal effect, which might be produced by traces of mercuric bichk)ride 

 untreated seeds were inoculated with spores, divided into two lots and sub- 

 jected to drying. Platings were made from the first lot while seeds from the 

 second lot were planted in pots at the end of every seventh day. Platings 

 gave, substantially, the same results as obtained in previous experiments. 

 In the first three plantings of seeds, infection was produced in the seedhngs; 

 the fourth planting gave negative results, and subsequent plantings failed 

 to produce infection in the seedlings. 



These results merely indicate that free spores exposed on the surface of 

 celery seeds, are not able to survive desiccation at room temperature for a 

 period longer than 30 days. Because of the many varying factors, these 

 tests cannot be taken as an accurate index as to the time which must elapse, 

 before infected seeds may be considered safe. Spores used in the above 

 experiments were produced in pure culture. Under such conditions, there 

 is always the possibility of the spores being less resistant than those produc- 

 ed on the host plant. Under natural conditions, the spores discharged are 



