a disease of cupressus plants. 615 



The Organism in Artificial Cultures. 



Artificial cultures of the organism were obtained 'by 

 thoroughly washing portions of diseased tissue in running water, 

 and partially immersing them in prune agar. From the growth 

 which developed on these, portions were transferred to fresh 

 plates of the same medium, and on these Phoma pycnidia 

 developed. Mature spores from these were then planted out, 

 and resulting single spore colonies were transplanted to different 

 media. The medium on which the organism grew most success- 

 fully was prune agar, although carrot, beef-broth, potato and 

 cornmeal agars were also used with good results. In all cases 

 except beef-broth agar, growth was regular but not zoned, scanty^ 

 matted, and of a greyish-green colour. Pycnidia began to develop 

 abundantly on the third day after the spores were plated out, 

 and were mature on the fifth or sixth day, the spores oozing 

 out in a pale salmon-pink drop, which emerged above the ve.o"eta- 

 tive growth. The pycnidia originated in the matted hyphae of 

 the aerial growth, but at maturity were found to be embedded in 

 the substratum. The growth on Beef-broth agar dift'ered in 

 being white, while the pycnidia were also of a white translucent 

 colour ; otherwise growth was the same. The optimum tempera- 

 ture .was found to be about 25° C. Growth at 20° C. was very 

 slow, and the formation of pycnidia was retarded. 



Viewed microscopically, the pycnidia formed in artificial 

 cultures were usually globose and beaked, with a definite ostiole. 

 From the latter the spores oozed out in a vermiculate manner, 

 and were rather more oval in shape than when occurring natur- 

 ally {PL 20, a). 



Germination Test. 



Hanging drop cultures of spores produced in culture were 

 made in Ward tubes and incubated at 25° C., at which tempera- 

 ture they germinated readily in 24 hours. On germination, the 

 spore swells up considerably, and often divides into two, a tube 

 being given off either from both ends or from one only. These 

 tubes continue lengthening, but only occasionally 'branch. No 

 secondary spores were observed to form. (PI. 20. h.) 



Inoculation Experiments. 



Inoculation experiments made in 1915 on C. toriilosa and 

 C. arizonica failed to produce infections in plants not first 

 wounded, and injured plants were only infected under very wet 

 conditions. In experiments recently conducted on young plants 

 of C. macrocarpa, 25 per cent, infections were obtained on un- 

 injured plants under moist conditions. So per cent, on injured 

 plants under moist conditions, and no infections on plants kept 

 under normally dry conditions. 



The experiments were carried out on the following lines : 



(i) Plants were sprayed with water containing a heavy 



suspension of spores^ or were sprayed with water 



. _ alone and the spores painted on, and were then kept 

 in a moist chamber for a week. 



