246 PHYTOPHTHORA MEADII n. Sp. ON HEVEA" BRASILIENSIS 



medium and on the sides of the tube. They have never been seen to discharge 

 zoospores when they are not in contact with water though many attempts 

 have been made to induce them to do so. When they germinate at all in these 

 conditions they do so as conidia. Sporangia are mostly pear-shaped with the 

 sporophore attached at or near the middle of the blunt end. In such water- 

 cultures they vary from 17 to 44jj x 15 to 29/u,, the average being 32 X 23/^. 

 At the narrow end is a protuberant, blunt papilla which consists of a hyaline 

 thickening of the wall. The apex of the papilla and the thickening below it 

 dissolve when the zoospores are on the point of emerging, and an opening is 

 thus provided through which they pass. Sometimes a sporangium has two 

 apexes and only one or both of them may be concerned in the discharge of the 

 zoospores. In water-cultures from vigorously growing hyphse that have been 

 taken from a young culture or from the mycelium that has just emerged on 

 the surface of the plant in nature, sporangia are fairly uniform and symme- 

 trical, while especially in older well-infected fruits and in old nutrient-agar 

 cultures the variation is considerable. On fruits and on old French-bean-agar 

 cultures they may be broadly or narrowly pear-shaped or elliptical and occa- 

 sionally come near being spherical. They may be bent (PL II, fig. 6) or even 

 hour-glass-shaped (PI. II, fig. 4) or very occasionally lobed (PI. II, fig. 5.) 

 On fruits the sporangia vary from 33 to 67 fx x 14 to 28/x, the average being 

 48 X 21 /A, while in French-bean-agar cultures they vary from 33 to 

 72/i X 20 to 41/A, the average being 48 x 30/x. Thus both in nature and in 

 culture the sporangia are considerably larger than those developed in 

 water-culture. This, however, is due to the different conditions ip. which 

 they grow. WTien they develop submerged in sufficient water they come to 

 maturity and discharge more rapidly than they do in the " drier " conditions 

 in which they develop in nature and in culture tubes. 



A typical sporangium is attached at the blunt end symmetrically to its 

 sporophore ; but the latter is placed in many cases more or less to one side, 

 e.g., PI. II, figs. 1,3, 4, 5, and in extreme cases may come comparatively near 

 the apex, e.g., PI. II, figs. 6 and 13. Sporophores vary considerably in length. 

 In water-cultures they are usually long varying from 10 to 200/^ and they may 

 be as long as 960)W. In nature and on inoculated fruits and leaves they are 

 often quite short, and very occasionally the sporangium is sessile. When 

 they are short the br,anching of the sporangiophoies, can be made out, but 

 when they are long it is, as a rule, impossible to trace them far enough in the 

 weft of hyphse in which they lie. The branching is sparse, usually from 5 to 10 

 sporangia occurring on a branchlet. The sporangiophores are not distinguish- 

 able from ordinary hyphse except by the pret-ence of sporangia. Their diameter 



