VEGETABLE SAP. 123 



apparent early in the summer, and therefore is as 

 valid proof of descent in the month of May as in 

 September or October. Bulbs, tubers, and tuberous 

 roots begin swelling- early in the season, and continue 

 increasing till the growth ceases in the autumn ; 

 consequently there must be something like a current 

 down as well as upward. This is, however, one of 

 the most inexplicable phenomena in vegetable 

 economy. 



It is quite evident that all the parts of a plant, 

 root, stem, and head, are enlarged together during 

 the summer, and mainly by the nutriment taken in 

 by the roots, and which food, of course, ascends to 

 the parts above and descends to the parts below the 

 roots, as in the case of potatoes. In watching the 

 gradual enlargement of the stem, we cannot avoid 

 observing, that there is a processional maturation or 

 enlargement of the parts, beginning, as it were, at 

 the top, and proceeding downward, not only to bulbs 

 and tubers, but to the fibrous roots of trees also. 



In order to have a clear understanding of this 

 curious circumstance, it is only necessary to state 

 the facts as they occur to practical observation : If 

 a shred remains too long in the same place on the 

 stem or branch of a trained tree, it causes constric- 

 tion, which not only obstructs the growth of the 

 part covered, but produces an unnatural prominence 

 on each side of the band, and much more above than 

 below. (Fig. 36.) This result shows that some com- 

 ponent or internal motion of the plant is obstructed 



