252 PHYTOPHTHORA MEADII n. sp. ON HEVEA BRASILIENSIS 



that they were not fully mature, as the colour was pa!er, and they were found 

 unexpectedly early in the season. As moulds develop rapidly on stored rotting 

 fruits, all except those searched for oof^onia were put in piclde, so the chance 

 of examining them at a later stage of development was lost. On the fruits 

 collected on lOth August, 1917, twenty-two oogonia with oospores were found, 

 eleven from the soft mesocarp and eleven from the outside of the endocarp. 

 The oospores of those found in the mesocarp were of a lighter tint, and were 

 probably not mature, and this is borne out by the fact that both oogonia and 

 oospores were on the whole smaller than any others found on fruits. The 

 oogonia and oospores from the endocarp were the largest found on fruits, being 

 a little larger than those seen in September, 1916, and they come nearer those 

 that developed in culture. Some of those oospores were more deeply tinted 

 than any hitherto seen, being almost brown and difficult to see through. As 

 in the case of the four spores without an oogonial covering seen on the fruits 

 examined on 7th September, 191 6, so here too a few spores were found that had 

 no surrounding oogonial-wall. On the last occasion twenty-two of them were 

 measured, and they varied from 20 to 29/a y. 19 to 28/a, their average being 24-5 x 

 24/x. Their limits are within those of the oospores found on the same fruits, 

 though their average is a little higher. They were found on the outside of 

 the endocarp, the tissue surrounding them having to be teased out on thfe 

 slide in order to make a microscopic preparation. They have exactly the 

 appearance of oospores in colour, thickness of wall and appearance of the. 

 contents, and I think that they are oospores from which the oogonial-wall had 

 decayed, or had been removed mechanically in making the preparation. 

 Such spores have not been observed in culture, where the same difficulty of 

 manipulation in making a microscopic preparation does not exist. 



The variation in size of 136 oogonia and oospores found in culture on 

 French-bean-agar is for oogonia 22 to id/x y. 20 to 45/a, and for oospores 16*4 

 to 32)mx15 to 32/A, while that of 79 found on fruits in nature is for oogonia 

 20 to 48/^ X 20 to 40/x, and for oospores 16 to 32/a x 16 to 32/^-, so that the limits 

 of variation in the two cases are close. The average, however, for those in 

 culture is higher than that for those in nature, the average in the former 

 case being for oogonia 33 x 31/j^, and for oospores 25*5 x 25/a, and in the latter 

 case for oogonia 25x24-6/* and oospores 21x20*5/a. On the last occasion, 

 however, on which oogonia and oospores were found on the endocarp of the 

 fruit, the average of the eleven seen was for oogonia 30*5 X 29"7it*, and for 

 oospores 23*6 X 23'5iu,, and this average approaches much nearer that in culture. 

 Seeing that so few were found on the fruits, every one distinctly seen was 



