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TRANS. ST. LOUIS ACAD. SCIENCE. 
either a few stomata, often difficult to discover, or, rarely,'numer¬ 
ous ones; so that in this interesting species the question arises 
whether the presence or absence of stomata alone can specifically 
separate forms otherwise scarcely distinguishable, as that acute 
observer of these plants, A. Braun, has maintained, or whether 
the stomata do not always play that important part in classifica¬ 
tion generally assigned to them. Below will be found directions 
for the investigation of the stomata. 
The parenchyma of the leaf consists of a few or several layers 
of chlorophyll-bearing cells, i. under the epidermis, 2. around 
the central bundle of vessels, and 3. forming the dissepiments, 
which cross each other in the centre of the leaf. 
An important element in the leaf structure is found in the peri¬ 
pheral bast-bundles, which are present in some and absent in 
other species ; and their presence often, but not always, coincides 
with the presence of stomata. When present they commonly 
form four bundles, two in the two anterior angles of the leaf, 
and two where the median dissepiments connect with the ante¬ 
rior and the posterior wall of the leaf; in I. Nuttallii I find 
•only three bundles, the anterior median one being wanting; in 
I. Cubana six bundles are visible, the two additional ones being 
located where the transverse dissepiment unites with the outer 
wall. In some rigid-leaved land species, e.g. I. melanopoda , 
often several smaller accessory bundles are found scattered under 
the epidermis. 
The examination of the fresh Isoetes leaf is not very difficult; 
particles of the epidermis are easily removed and show the 
stomata, when present, very distinctly. Where there are few 
stomata, the epidermis from different parts of the leaf must be 
examined, and especially from the tip, as they are more apt to 
r be found there. In dried specimens the leaf must be soaked, the 
algoe which often adhere to the surface have to be carefully 
scraped off, after which I make several sections 1 or $ line wide, 
lay them open by a vertical slit, detach the central bundle, and 
then scrape Very gently the inner surface so as to remove the par¬ 
enchymatous cells which obscure the appearance of the stomata 
This process can be aided by an immersion of the specimen in a 
weak solution of caustic potash. The work is often a difficult 
one when the specimen is very old or poorly preserved, and 
