ON SAP. 71 



r , 



Emily. And how do you account for so remarkable a 

 difference in the result of these experiments ? 



Mrs. B. Chiefly from the improved mode of perform- 

 ing them. The velocity of the sap varies, however, very 

 considerably, owing to a variety of causes : the nature of 

 the plant, the degree of temperature, and, above all, the 

 quantity of solar light ; which last is absolutely required 

 to enable the leaves to evaporate the superfluous water. 



During the spring there is a more than usual absorption 

 of sap, for the purpose of nourishing the young buds 

 which are to be developed ; and it is very worthy of re- 

 mark, that the sap which feeds these buds passes through 

 different channels from that which serves to nourish the 

 plant generally. Instead jof rising through the young 

 wood, it ascends nearly in the centre of the stem, in the 

 parts contiguous to the medullary channel, and is thence 

 transmitted, by what means is not yet ascertained, through 

 the several layers of wood to the buds. 



Emily. But the sap that nourishes the buds which first 

 shoot in the spring, cannot have been passed through the 

 leaves, and undergone that change which you say is ne- 

 cessary to convert it into appropriate food. Can it feed 

 the buds in the crude state in which it rises in the stem ? 



Mrs. B. There is great reason to suppose that it is 

 in some measure elaborated during its passage from the 

 roots to the buds ; probably by the organs which it tra- 

 verses in passing laterally from the centre to the circum- 

 ference of the stem or branch ; but it is a point very diffi- 

 cult to ascertain, owing to the extreme minuteness of 

 these organs : it is, however, a very reasonable inference, 

 since the sap, when it reaches the buds, is in a state ready 

 to be assimilated to their substance. 



Part of the sap, which rises in the month of August, 

 in all probability follows the same course, being destined 

 to nourish the new buds which shoot at that season ; but 

 it is less abundant than that of March, having fewer bucte 

 to bring forth. 



381. How is the remarkable difference in the result of these experi- 

 ments accounted for'? 382. What is sard of the quantity of sap ab- 

 sorbed in the spring 383. In what part of the stem does it ascend 

 384. Emily asks if sap can feed the buds in the crude state in which i 

 rises in the stem what is the answer of Mrs. B.I 385. What is sai 

 of the sap which rises in August! 386. Why is it less abundant tha 

 in March! 



