ENGELMANN-THE GENUS ISOETES IN N. AMERICA. [3 6f 
IO 
requires a good deal of patience. Sometimes the application 
of iodine will very distinctly show the stomata by coloring their 
guard-cells blue when only these contain amylon, but jo f course 
not when the other cells'are also filled with that substance. A 
magnifying power of 150 to 250 diameters is best adapted to well 
exhibit the stomata. 
To find the bast-cells it is necessary to make the thinnest pos¬ 
sible transverse sections of the leaf, boil them well, and, if they 
do not then show under water as bundles of minute, thick-walled,. 
darkish cells close to the epidermis, very distinct from the much 
larger epidermis cells, the application of a solution of caustic pot¬ 
ash, to clear the preparation, will readily bring them out. The 
same magnifying power which we use for the examination of 
the stomata may be applied for the study of the bast-bundles. 
I would advise anyone who desires to study the structure of 
Isoetes leaves to commence with well known species and good 
(if possible fresh) specimens, and make himself familiar with the 
manipulation and with the appearance of their parts under the 
microscope before he proceeds to study unknown and difficult 
specimens. 
The arrangement of the leaves in the species with two-lobed 
trunks is at first distichous, and in I. melanospora it remains so- 
through life ; in all the others the leaves soon enter into a more 
complicated phyllotactic order; in the larger ones, with many 
leaves the and even the order is found. 
The number of leaves varies from 5 or 10 {I. pygmcea, I. me - 
lanospora) to 100 or even 200 (/. Engelmanni , var. valida), 
and their length from £ to 1 inch (in /. pygmcea) to 1-2 feet (in 
some forms of /. Jiaccida and I. Engelmanni) ; their color from 
light and fresh yellowish-green (I. Engelmanni) to dark and 
dull green I. lacustris) ; their rigidity is greatest in the terres¬ 
trial species, and also in some submerged ones ; and least in most 
amphibious species, which often float their leaves on the surface 
of the receding water, or in some submerged ones, the leaves of 
which, taken out of the water, collapse like the soft hair of a wet 
pencil. Th6 submerged species vegetate and retain their verdure 
throughout the winter (whence, it is said, the name of the genus- 
is derived : Isoetes , equal at all seasons), but the others lose their 
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