MOVEMENTS OF SAP. 173 



perennials continne for an indefinite but variable period, ac- 

 cording to the nature of the species. 



We are now prepared to consider the subject of the circu- 

 hition of sap in the entire plant, involving two topics about 

 which there have been much controversy and speculation, 

 and too little observation and true philosophy. The first re- 

 lates to the ascent of what is styled the crude sap, which 

 enters at the root, and rises against the force of gravitation 

 to the topmost leaf of even the tallest tree. The other has 

 reference to the return of the so-called elaborated sap from 

 the leaf to the root, so as to complete a true circulation. 



Many have said there is no such thing as a general circula- 

 tion of sap ; but no one doubts the fact of an upward flow 

 from the roots, and a vast exhalation of water from the foli- 

 age, during the period when the vital forces of the plant are 

 active. It is also universally admitted that the cells contain- 

 ing chlorophyl are the organs in which the elements of the 

 carbo-hydrates are combined, and from which, therefore, they 

 must pass by some channel to all other parts of the plant, 

 where either growth occurs or amyloid substances are stored 

 up for future use. Whether the albuminoids are formed also 

 in the cells of the leaf or are the result of combinations oc- 

 curring in the cambium between the soluble carbo-hydrates 

 and the ingredients of the crude ascending sap is not certain, 

 and has no necessary connection with this discussion. The 

 distinguished botanists who have devoted themselves to the 

 study of vegetable structure and physiology have generally 

 erred in one of two directions. Some have attempted to re- 

 duce the phenomena of plant-life to systems of their own in- 

 vention which were the results of imperfect and partial botan- 

 ical observations and a limited knowledge of the collateral 

 sciences of chemistry and physics, while others have endeav- 

 ored to explain all the mysteries of the vegetable organs and 

 their functions by the general application, without the experi- 

 mentum crucis of the various principles of science which are 

 known to govern the changes occurring in dead matter. 



Thus Coesalpinus, without possessing any definite knowledge 

 of organography or chemistry, regarded the pith as the seat 

 of life and the source of all the veins through which circula- 

 tion went on, while the leaves he thought to be chiefly useful 



