Laboratory Notes. 
l 9 I 
LABORATORY NOTES. 
SOME SIMPLE PHYSIOLOGICAL DEMONSTRATIONS. 
BY 
F. E. Fritsch, D.Sc., Ph.D., 
Professor of Botany, East Loudon College, University of London ; 
AND 
E. J. Salisbury, B.Sc., 
Lecturer in Botany, East London College, University of London. 
[With One Figure in the Text]. 
I N connection with a course of lectures recently given by one of 
us, a number of simple methods of physiological demonstration 
have been worked out, some of which seem to us to be of sufficient 
interest to warrant a brief description. 
1. An artificial stoma. —Diverse models of stomata constructed 
of unequally thickened rubber are described by various authorities, 
but none of these are easily made, the materials are somewhat 
costly, and moreover, the results are not always satisfactory. The 
artificial stoma about to be described, though open to certain 
objections, has the great advantage over rubber-models that it can 
be made at any time and in the space of a few minutes. To 
construct such a model the stem of an herbaceous plant provides 
all the material that is required. We have found the scape of a 
jonquil, Narcissus or daffodil, and particularly the internode of the 
dog’s mercury ( Mercurialis perennis) to be perfectly satisfactory ; 
the petiole of the cuckoo-pint ( Arum maculatum) and the internode 
of the dead-nettle also furnish suitable material. A straight piece 
about three to four inches long (in the case of the dead-nettle one 
to two inches long) is selected and is halved lengthwise. The two 
halves thus obtained are then placed in strong salt solution until 
they become flaccid. They are thereupon placed parallel to one 
another in such a way that the original outer surfaces of the 
internode or scape are in juxtaposition, while what was previously 
the inner surface faces outwards. In this position the two halves 
are firmly tied together by string at their two ends (Fig. 1, B, a). 
If the two pieces thus joined together are placed in tap water, in 
the space of a few minutes they will (as they gain in turgescence) 
arch apart so as to leave a wide aperture between them (cf. Fig. 1, B, b) 
—in other words the pore of the artificial stoma opens. A return 
to the salt solution again results in the closure of the pore, and this 
sequence of events can be repeated several times. If the artificial 
stoma with the pore widely open is allowed to dry slowly by exposure 
to the air, a marked decrease in the width of the opening becomes 
manifest after some time, although the closure is not so complete 
as when due to plasmolysis. 
