6 A. Barclay — On a TJredine affecting the [No. 1 



age of the needles. The sheath cells are considerably longer than they 

 are broad. They do not contain chlorophyll but often large starch 

 grains. Within the endodermic sheath are first thin- walled parenchyma 

 cells, with sinuous outlines opposite the xylem, but more cubical opposite 

 the phloem. These cells have large bordered pits. The xylem is to- 

 wards the upper side and the phloem below it. The xylem is more or 

 less distinctly divided into two lateral halves by two to three or more 

 large thick- walled sclerenchymatous cells. The phloem is more distinctly 

 divided into two lateral halves. Beyond the phloem is a group of from 

 three to seven large thick- walled sclerenchyma cells, and, in the centre of 

 this, immediately adjoining the phloem, one large empty thin- walled cell 

 may always be seen. 



(b) Microscoj>ic Characters of the ^cidial Fungus. — The general 

 appearance of the invaded tissue of a needle in a transverse section is 

 well shown in fig. 22, and, if this be compared with fig. 21 (exhibiting 

 a transverse section of a normal needle), the general deviations in 

 the structure of the former from the normal condition are at once 

 apparent. The parenchyma cells are larger and rounder than in the normal 

 condition. They measure from 0*1 77 or O'lOl m.m. in length by 0"058 

 in width, whilst in the normal needle these dimensions are from 0"093 

 or 0*071 by 0*035 m. m. The radial arrangement of these cells is also 

 entirely lost, and no vestige of the resin canals remains. The most stri- 

 king change, however, produced in the invaded tissue is the separation 

 or dislocation of the parenchyma cells from one another by the mycelium. 

 In every transverse or longitudinal section of a needle, it is easy to trace 

 the course of the mycelial filaments for a short distance in the paren- 

 chymatous tissue (figs. 5 & 6). In these figures, it will be observed 

 that, though both are magnified equally, the liyph^ of the one are 

 greater in diameter than those of the other. The cause of this differ- 

 ence is due to their different treatment and mounting. Fig. 6 re- 

 presents a section which was stained in picrocarmine and immediately 

 mounted in Farrant's gum solution, whilst the section represented in 

 fig. 5 was stained with vesuvin, then immersed in absolute alcohol, 

 cleared in clove oil, and mounted in Canada balsam. I had no oppor- 

 tunity of examining the tissues when they were quite fresh, and the 

 following measurements of the diameter of the hyphoe are therefore 

 subject to correction. The diameter of the filaments illustrated in fig. 

 6 (mounted in gum) was on an average 4-7/a, whilst the average diameter 

 of those represented in fig. 5 was S'l/x. The mean of these two measure- 

 ments would probably very nearly approach a correct measurement of 

 the fresh filaments, for, whilst the former measurement may be a little 

 excessive from absorption of water, the latter is probably reduced by 



