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122 MISSOURI BOTANICAL GARDEN. 
mixture warms the frost first leaves the bottom of the jar, 
moving in a band toward the top. At the appearance of 
this symptom it is usually found advisable to refill the 
jar, as procedure, after this point is reached, is usually slow 
and uncertain. Again, after connecting the terminals of 
the reversing key, care should be taken not to handle the 
stirrer until all traces of oil have been removed from the 
hands, and splashing of the freezing mixture on the couple 
should be avoided for very obvious reasons. Perfect cleanli- 
ness and care should be exercised throughout the test. 
While all of the above is more or less a repetition of 
the directions for using the apparatus as given by Messrs. 
Dixon and Atkins, still it seems necessary to repeat such 
essentials as have been given here. 
Altogether, some 110 species of plants (trees and shrubs) 
have been gathered, and of these only 90 have been finally 
tested out, owing to the inability of getting sap from some, 
and to its viscidity in others, thereby preventing its use in 
the small tubes containing the couple. The plants whose 
saps, for one reason or another, could not be used in the 
tests are as follows :— 
Crataegus prunifolius Paulownia imperialis 
Pyrus japonica Sassafras officinalis 
Acer platanoides Ulmus campestris 
Aesculus Hippocastanum Acer laetum rubrum 
Quereus imbricaria Amorpha fruticosa 
Pyrus arbutifolius Euonymus atropurpureus 
Acer saccharinum laciniatum Hydrangea radiata 
Ulmus alata Ampelopsis quinquefolia 
Leitneria floridana Spiraea prunifolia 
Tilia americana 
Owing to the slow process of sap extraction and the limited 
time at the disposal of the writer, it was found necessary 
to carry the experiments along in sections, i. ¢., the plant 
leaves were collected from 20 to 30 species at a time, the 
saps pressed out by means of a vise, after first being bruised 
in a mortar and wrapped in muslin which had been shrunk 
several times. Steel plates, which are shown at the left 
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