W. MCRAE 231 



between the three carpels, and thence through the hiliim into the seed. The 

 endosperm and embryo are rapidly permeated. Soft and watery by nature, 

 the endosperm forms an excellent pabulmn on which the fungus increases 

 rapidly. It gradually shrinks till it becomes a thin remnant adhering to part 

 of the inner wall of the testa. The remaining space is sometimes partially 

 occupied by a copious growth of hyphae as is also not infrequently the loculus 

 between the endocarp and the testa. Hyphse are found in the hard endocarp 

 where they pass from cell to cell chiefly through the pits on the cell-wall. 

 Their diameter being usually greater than that of the pits, they contract as 

 they pass through. The endocarp, however, remains hard, and only a thin 

 layer of the outside surface disintegrates and softens, and here sometimes 

 oogonia are produced. In a similar way the hyphas penetrate the tissue of the 

 testa, but it, too, remains hard and brittle. From the axis of the fruit, hyphse 

 pass through the tissues of the fmit-stalk in the same way as they do through 

 a branch. 



Hyphae of Phytophthora occur in all the tissues of the branch, and are found 

 both in the cells and between them. They are specially abundant in the 

 medullary rays, and sometimes give them the appearance of white streaks in 

 the wood. In the cortex they pass through the cell-wall at any point, but 

 in tissues that have thick-walled cePs, they, as a rule, pass through the cell-wall 

 at a pit becoming narrower in diameter as they pass through. They have not, 

 however, been found in the thick-walled stone cells of the cortex. Usually they 

 are from 3 to 6/ji in diameter, but in the pith they are sometimes up to 10/x with 

 branches of considerably smaller diameter arising from them. On the dis- 

 coloured areas of bark on the recently tapped surface of the stem, the cell- 

 walls become yellow and the cell-contents brown. The cells collapse and 

 become irregular in outline, thus leading to the contraction and rupture of the 

 tissue as a whole. Hypha) of Phytophthora are found between and in the 

 cells of the inner part of the hving bark. They are, however, fewer and 

 more difl&cult to find in this position than in any other part of the tree. The 

 fungus gets into the branch in three ways, through the fruit-stalk, through the 

 leaf -bud, and through the green twigs. H>^hi» pass directly from the 

 tissues of the stalk of an infected fnut into the connected tissues of the 

 branch from which it sprang. Six weeks after the fruit-rot had been first 

 observed on a tree, the stalk of an infected fruit had become discoloured 

 to within half a centimetre of its insertion on the branch. Hyph» were 

 found throughout the stalk in cortex, vascular tissue, and pith. They had 

 peneti'ated into the cortex, wood, and pith of the parent branch, and in a 



