222 PHYTOPHTHORA SP. ON HEVEA BRASILIENSIS 



the zoospores produced iu culture media is almost the same as those produced 

 on the host plant. The resting conidia in nutrient media do not show as much 

 variation as the sporangia. They are only slightly bigger than those found 

 in nature. 



In water cultures the branching of sporangiophores is as complex 

 as those of Ph. omnivora ; sporangia are of the same size as those found on the 

 host plant. 



The fungus grows luxuriantly in French bean juice agar, Quacker oat agar, 

 Oat juice agar, Gram agar, and Green peas agar. In these media the aerial 

 growth is very profuse, the culture tubes being completely filled by it 

 within a week, 



In glucose meat-extract agar the mycelium remains submerged and forms 

 on the surface a thick undulating mat. The hyphse are richly branched, 

 irregularly swollen and full of highly granular protoplasm and oil globules. 

 Sporangia and resting conidia are fairly numerous. 



If this culture medium contains a trace of potassium phosphate the fungus 

 remains sterile. Instead of this salt if one per cent, tannic acid be added the 

 growth is similar but sporangia and resting conidia are produced in abundance. 

 The colour of the resting conidia varies from deep honey to light yellow. 



Klebs^ and Kauffman^ have found haemoglobin to be one of the best sub- 

 stances for the formation of sexual organs in SaprolegniacecB. In solutions 

 of 0*1 per cent, and of 0*05 per cent, haemoglobin and of 0*1 per cent, haemo- 

 globin with 0"1 per cent, of peptone and of 0*05 haemoglobin with 0*02 per cent, 

 peptone the Phytophthom under study did not produce these organs. The 

 growth was rather poor. The mycelium remained settled at the bottom of 

 the solution like a woolly ball. The mycelium was branched ; sporangia and 

 resting conidia were fairly abundant. 



As in liquid solutions the growth of the fungus is rather poor, 0*1 per cent, 

 haemoglobin was added at about 50°C. to sterilized French bean juice agar 

 and Oat juice agar. The growth of the fungus was good. Sporangia and 

 resting conidia were j)roduced in large numbers. Resting conidia formed 

 near a granule of haemoglobin were generally deeply coloured, dark brown 

 or deep honey-coloured ; no sexual spores were produced. Traces of potassium 

 phosphate and calcium nitrate were added to French bean juice agar with 



1 Klebs, G. Zur Phyeiologie der Fortpflanzung einiger Pilze II Saprolegnia mixta. Jahrb. 

 Wiss. Bot. xxxiii, 1899. 



2 Kauffman, C. H. A contribution to the Physiology of the Saprolegniacecs, with special 

 reference to the variations of sexual organs. Ann. Bot. xxii, 1008, p. 362. 



