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NEW YORK, MARCH 23, 1894. 
THE IMPORTANCE OF STRUCTURAL DETAILS 
IN THE STUDY OF PLANTS. 
BY W. W. ROWLEE, ITHACA, N. Y. 
Ir there was any one thing more than another that led 
the ancient herbalists into serious and often amusing 
errors in regard to plants, it was their ignorance of the 
structure of vegetable tissues. Their minds were not in 
a condition to be attracted by natural phenomena, and, 
further, they were without lenses and other appliances 
which are so indispensable as aids to workers of the 
present day. 
_ It is, moreover, but recently that some important ad- 
vances have been made in methods of treating tissues in 
order that their structure may be more thoroughly and 
exactly studied. With the exception of those which are 
lignified or sclerenchymatous, all vegetable tissues are too 
soft and yielding to be cut even with the sharpest knife 
without undergoing displacement and distortion, and 
especially is this true of that part of the tissue most im- 
portant of all froma physiological point of view, 1. e., 
the protoplasm. In its normal condition in the vegetable 
cell, protoplasm resembles in texture and consistency the 
white of an egg. No one would expect to cut this sub- 
stance in its natural condition into sections to be examined 
with a microscope. ‘The cell-walls also are displaced 
when unfixed tissue is cut, especially if the tissue be 
from delicate organs. If fresh material could be cut and 
examined without any distortion it would be highly desir- 
able to do so, as all parts would be unchanged, but not 
only is this impracticable on account of the firmness of 
the tissue, but, moreover, certain parts are in nature 
colorless and must be stained before they can be seen. 
Fixation of tissues consists in hardening and preserving 
the pliable and perishable parts of tissues, especially pro- 
toplasm and its primary modifications. This is accom- 
plished by replacing the water in the tissue by some pre- 
serving fluid, The tissue must be killed immediately, 
and the elements must remain 77 sztu through the process 
of infiltration if the fixing is properly done. Professor 
Gage in his ‘‘Histology” recommends picric-alcohol 
(25 p. c. alcohol + .2 p. c. picric acid) for fixing tissues, 
and it has given us entire satisfaction so far as fixing 
material is concerned. The stain made by picric acid, 
however, is not altogether satisfactory. Professor Camp- 
bell (Bot. Gaz. Feb., 1891) found chromic acid very 
effective as a fixing agent in his work upon the delicate 
tissues of fern prothallia. We have been satisfied with 
results attained from using alcohol, always being careful 
at first to apply only sufficient to kill the tissue and then 
gradually to increase the strength of alcohol until the 
tissue is completely dehydrated. The most satisfactory 
method of accomplishing this we have found is by the 
modification of Schultze’s apparatus devised and de- 
scribed by Professor Thomas (Proc. Am. Micro. Soc., 
1890). If the fixing has been properly done all the tissue 
elements will be zz sf and normal except in so far as the 
alcohol produces changes. The tissue after fixing has 
been accomplished instead of being flexible is exceedingly 
brittle and must during succeeding manipulations be 
handled with the greatest care. As a general rule it is 
safer to pour pieces of delicate tissue from one vessel to 
another rather than to handle them with forceps. In 
this condition, protoplasm and cell-walls are firm enough 
to withstand the knife without displacement, providing 
proper support is afforded. 
This support may be gotten by infiltrating the tissue 
with some liquid which under changed conditions will be- 
come solid. Here, too, the agents used should be such 
as modify the tissue as little as possible. Paraffin and 
collodion have been most used. Both will penetrate not 
only the intercellular spaces and cell cavities but will also 
infiltrate into the cell-walls and protoplasm, preventing the 
former from tearing and holding the nucleus and plastic 
bodies of the latter in position during sectioning. The 
effects of alcohol and other reagents upon tissues should 
be determined carefully by experiment, and such changes 
as occur should be considered before conclusions are 
drawn. 
The importance of exactness in structural studies can 
scarcely be over-estimated. Confirmation or modification 
of new systems of classification (and there are plenty of 
them at the present time) must depend for their per- 
manency quite as much upon accurate observation of 
structural details as upon the ingenuity of any system- 
atist. A single illustration from a discovery made in our 
laboratory may not be inappropriate. The nodding 
bidens (Bidens cernua) differs from its congeners of the 
northeastern United States in having the hypocotyl of 
the embryo in the seed before germination possessed of 
large and numerous intercellular spaces. The occurrence 
of large intercellular spaces in an embryo is of com- 
paratively rare occurence and is probably of assistance to 
the plant in aerating its tissues during germination. This 
seems the more probable when one considers that the first 
structural modification attending germination is the en- 
largement of the intercellular spaces. In species in 
question the provision of intercellular spaces has been 
provided before germination. If this organ had been cut 
fresh the knife would have displaced the cells so as to 
render uncertain the relation of the cells and spaces. 
