322 Professor Marshall Ward , On the Question of 
packed stomata were cut through twice, or two stomata on the 
same row occurred in the thickness of a section, or a stoma was 
merely shaved b} 7 the razor, and such were apt to be missed in 
the counting, and so on. The numbers thus obtained were only of 
use in establishing generally the fact that those above are more 
numerous than those below. 
On the whole, useful though the above methods were for 
checking results, there were considerable divergencies, and the 
best way was found to be that of carefully counting the stomata 
on a given area somewhat larger than one square millimetre, and 
plotting them out on squared paper. On then placing over the 
chart a glass plate, covered all over except a square repre- 
senting, on the same scale as the paper, one square millimetre, it 
was easy to count the stomata in five positions of the square and 
obtain more correct results (see Table IV.). 
I may add that I checked this last method, so far as B. mollis 
is concerned, by repeating it on a seedling germinated in December, 
and at a much lower temperature and under very different con- 
ditions as regards illumination, &c. On the upper surface the 
number of stomata, 35 per square millimetre, was the same as 
before, though that of the hairs was fewer than the average. 
It only remains to add — so far as Table V. is concerned — that 
the measurements of the lengths of the stomata (column 1) were 
obtained from 10 measurements on each surface, and that I have 
given the extremes as well as the commonest lengths. The 
variations in breadth were too small to measure accurately with 
medium powers, and I concluded that as all the stomata appeared 
shut (except in the transverse sections) no data of value could be 
obtained from them. 
The next part of the plan adopted was as follows : 
Assuming that the number of experimental infections — 1846 
were employed — is large enough to warrant the procedure, I con- 
struct a curve of percentages of successful infections for each 
species with each kind of spore (see Table III.). Thus, with the 
spores obtained from B. mollis , B. mollis gave 70'6 °/ G , B. velutinus 
56*4 7 0 , B. secalinus 50’7 % °f successful infections, and so on. By 
joining the upper ends of ordinates proportional to these percent- 
ages, a diagram-curve is obtained which we may call the infection- 
curve. See Table VI. 
I then take the measurements of — say the sizes of the stomata 
— and construct a diagram-curve in similar manner of each of the 
measurements — extremes, commonest sizes, above and below — by 
joining the upper ends of ordinates proportional to the lengths, 
and taking the species in like order. 
It appeared that in this way it ought to be possible to express 
graphically any correspondences or discrepancies between the 
