in the Brontes and their Brown Rust . 307 
transverse sections, not too thin, in alcohol and glycerine to 
which water or eau-de-javelle are added in various proportions. 
The margins of all the species examined are strengthened 
by sclerenchyma-cells arranged in a long thin band, and a 
similar feeble band runs down the crest of the keel below 
the mid-ribs. In very rare cases a much feebler strand runs 
below the two stronger secondary bundles. In no case does 
the amount of sclerenchyma approach the dignity of a girder, 
as it so often does in the broader leaves of mature plants. 
The margins of all species examined, with the exception 
of one which is probably not a true Bromc, have short sharp 
asperities with the points turned upwards, sometimes with 
some turned downwards. Similar asperities occur also on 
the mid-rib or stronger ribs of B. unioloides , in addition to 
the hairs proper, but in no other Brome examined has this 
character been found to occur. 
13. Dimensions of the Leaf. 
Although differences of some value as regards length of 
leaf are attainable, so long as we confine our attention to 
seedlings growing under the same conditions, I pass them 
by as of relatively little importance in the present con- 
nexion. In Table XXIII are set forth the measurements 
of (1) the average breadth of the whole leaf ; (2) the number 
of ribs ; (3) the intervals between the ribs as measured on 
the translucent solid pieces of leaf ; (4) the same intervals 
as measured with a higher power on transverse sections ; 
(5) the average total breadth of the vascular bundles of the 
ribs, as measured on transverse sections ; (6) the depth of 
the mid-rib from the crest of its ridge above to the crest 
of the keel below ; (7) the depth of the leaf at the middle of 
the sinus between a pair of ridges, also, like the last, measured 
on the transverse section ; and lastly (8 and 9) the calculated 
sectional area of chlorophyll-tissue in each interval, and its 
volume for each square millimetre of leaf-surface. 
Columns 1 to 4 explain themselves. It is only necessary 
to remark that precautions were taken to compare any 
