INTRODUCTION TO BOTANY. xlix 



To account for the cause of the sap's rising, Richard sup- 

 poses a vital principle, to have a powerful influence; but other 

 internal and external causes may assist in promoting this rise, 

 for example, light, electricity, warmth, transudation inwards, 

 and outwards, 



3. Descent of the Sap 



Proved by tying a strong ligature to the trunk of a dicotyle- 

 donous tree, when a circular swelling will be produced above, 

 which will become gradually larger. The swelling can arise 

 only from the obstacle opposed to the juices descending, 

 through the cortical layers from the upper to the lower part 

 of the vegetable. The descending sap continually renews and 

 maintains the cambium, and it contributes chiefly to the 

 growth and developement of dicotyledonous trees. 



A striking difference exists between vegetables and animals ; 

 the former live almost exclusively on inorganic substances, as 

 water, carbon, hydrogen, oxygen, &c ; the latter on those 

 taken from the animal and vegetable kingdoms.' 



Organs of Reproduction. 



These are the flower, the fruit, and the different parts that 

 compose them : they serve for the preservation of the species. 



With regard to the calyx and corolla, Linnaeus gave the 

 latter name, corolla, to a single floral covering around the 

 stamens or pistils, or both, where the colours are vivid, and 

 the former name of calyx, where the colour h greeii. Jussieu 

 considers the single floral covering as a calyx, and gives it 

 that name of calyx, whatever be its colour, provided it be 

 single : others call the single floral covering a. perigonium ; for 

 example, the tulip. 



For a further account of the organs of reproduction 

 the reader is referred to Richard's Elements of Botany, by 

 Clinton, or Macgillivray. We will proceed to enter into an 

 examination 



' See all chemical terms, clearly explained in Parkes' Chemical Cate- 

 chism, &c. last edition, 



e 



