W. MCRAE 251 



immature, for the average of the measurements of oogonia is about the same 

 as that of those in other cultures, and the oospores are slightly larger. The 

 other cultures call for no special mention. 



Oogonia were found first in nature on three rotten and dried up fruits 

 gathered from the ground under Hevea trees on 6th September, 1916, and 

 examined next day. During the succeeding week about 300 fruits were 

 examined both on the trees and on the ground under them from the same 

 block and other blocks on the same estate, but no more oogonia were found. 

 On 20th June, 1917, twenty fruits picked from several trees on another estate 

 were found with oogonia. The pericarp of these fruits was soft and rotten, but 

 it had not then split along the six sutures. Forty other fruits collected at the 

 same time were devoid of oogonia. On 10th August, 1917, on a third estate in 

 another district oogonia were found on about 10 rotting fruits in a stage similar 

 to the last. On the fruits examined on 7th September, 1916, nineteen mature 

 oogonia with oospores were found immersed in the tissue of the mesocarp. 

 Round twelve of them the oogonial-walls were still present, three had remnants 

 of the oogonial-walls, and four had none. The epicarp of the fruits was soft 

 and rotten, consequently it was difficult to make microscopic preparations, so 

 I think that the oogonial-walls of these seven had been broken away either 

 partially or completely in the manipulation of the material, or they may have 

 diaantegrated within the tissue of the epicarp. There is the possibility, too, 

 that the last four never had oogonial-walls and were not oospores. This 

 supposition, however, is discounted by the facts that in cultures no thick- 

 walled spores have been found that are not oospores developed within oogonial- 

 walls, and that they agree in size, colouring and thickness of wall with the 

 oospores found on these fruits. The smallest oogonium with its oospore 

 measured 24-6x22'5/x and 20-5-j-20-5/x respectively; the largest oogonium 

 with its oospore measured 30-4 x 28/x and 28 X 26/* respectively. The averages 

 of the twelve were : oogonia — 25*5 X 24 "9/*, and oospores — 23-9 x 23*3/x. If the 

 three oospores ^vith incomplete oogonial-walls are taken into account, the 

 average of the oospores is 23'5x23/ii. The average of the 4 spores without 

 oogonial-walls is 23-8x23//; thus they agree very closely in size with the 

 oospores. 



On the fruits collected on the 20th June, 1917, 45 oogonia with oospores 

 were found in the mesocarp. The oogonia varied from 20 to 26/x x 20 to 27/x, 

 the'average being 23-7 x 23"5/x, while the oospores varied from 18 to 23m x 18 

 to 22/a, and the average was 20*3 X 20^. Both oogonia and oospores are 

 slightly smaller than those found on fruits in the previous year. It is likely 



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