Physiological Studies in Plant Anatomy 65 
and woody, and also with leafy twigs, etc. Particularly vigorous 
exudation pressure was developed by leafy twigs, Syringa ( Phila - 
delphus), species of Ribes, and Syringa vulgaris L., amongst many 
others, when inverted and immersed in water. With both stems 
and leafy twigs, instead of stripping off the cuticle or bark to enable 
the water to enter it was found sufficient to expose the stem and 
leaves to chloroform vapour for a minute or two. As a result the 
surface tension conditions at the stomata or lenticels were so modified 
that the water readily displaced the air and entered the stems at 
these points. 
Later reference to the literature showed that all the experiments 
of Pitra(i8) had been repeated and his observations of 1878 confirmed 
in practically every respect. This does not seem time wasted as 
Pitra’s experiments are but little familiar to the present generation 
of botanists. 
The following points in our experiments seem worth more detailed 
description as they extend Pitra’s observations in some slight degree. 
Boehm ( 4 ) criticised Pitra’s observations and explained the exudation 
of liquid as being due to gas developed in the xylem by fermenta¬ 
tion under the anaerobic unhealthy conditions in which the stems 
were placed. It is true that owing to the duration of many of 
Pitra’s experiments fermentation effects were very possible, and our 
attention had been drawn to them by obvious fermentation effects 
in our own experiments when of relatively long duration. However 
it is quite possible to get the effects seen by Pitra under sterile con¬ 
ditions. As already stated, our stems were usually placed in chloro¬ 
form vapour before mounting in water. This treatment could be 
rendered quite drastic, exposure for several hours to chloroform being 
without effect upon subsequent results. The vapour works inwards 
very slowly and quite thin stems require exposure for 48 hours to 
kill them. Stems then after rigorous treatment in chloroform were 
mounted under boiled distilled water in closed vessels, the stem 
emerging through a sterilised cork, and the tube above it containing 
a little sterilised water surmounted by a layer of toluol. Under these 
conditions the rise of liquid is still obtained and Boehm’s objections 
seem to be disposed of by experimental evidence. The fact that in 
many cases vigorous exudation of sap is obtained in less than 24 
hours also supplies strong evidence against the validity of Boehm’s 
criticism. 
Copeland ( 7 ) (loc. cit. p. 174) had already shown that Boehm’s 
objections were probably not well founded on theoretical grounds, 
5 
Phyt. xxi. 11. 
