OF SAP IN PLANTS. 37 



tity of fragments of wood remaining in, &c.) and the unequal 

 expansion of the wood must have ; a difficulty which I could 

 not master. Here, therefore, useful results could only be ob- 

 tained by a number of observations. 



II. THE SUMMER SAP. 



The circulation of the sap during the summer, at the period of 

 the greatest activity of the leaves, displays at once much agree- 

 ment with and many striking differences from that of the early 

 spring, among the latter of which stands above all the circum- 

 stance that the trees hitherto mentioned no longer bleed from 

 wounds inflicted on them, although, as a little reflection must 

 reveal, the quantity of fluid actually passing in the stem is far 

 greater; a fact also demonstrated by direct observation. 



In summer, as in spring, there exists a rapid ascent of the 

 crude sap ; in addition to this, a descent of unelaborated fluids 

 after every shower of rain ; and, lastly, a descent of the elabo- 

 rated fluids from the leaves into all parts of the plant. 



Since there apparently exists no means of tracing accurately 

 the mode and course of the last phenomenon directly, I have 

 restricted myself to the first, namely to the roads which the un- 

 elaborated fluids traverse in their ascent and descent in plants ; 

 but the results obtained could not but give ground for the de- 

 duction of many conclusions as to the behaviour of the elabo- 

 rated saps. The following pages therefore will be devoted to the 

 investigation of the paths by which the crude summer sap 

 ascends or runs down under conditions as natural as possible, and 

 afterwards also under various abnormally arranged conditions, 

 especially when wounds have been made in the plant. 



A. THE ASCENDING SAP. 

 1. With NORMAL, absorption of the Sap by the Root. 



For the purpose of tracing the course of the sap, the earth 

 round the plants to be experimented on was watered with dilute 

 solution of ferrocyanide of potassium ; after which cross slices of 

 the plant were tested for that solution with a mixture of acetate 

 of iron and hydrochloric acid. It is not advisable to make these 

 experiments on plants standing in the open ground, since the 



