52() THE REPRODUCTIVE FUNCIIONS. 



facts, which are well known to horticultiiralists, 

 exhibit only tlie capabilities of vegetative power 

 under circumstances whicli do not occur in the 

 natural course of things, but have been the effect 

 of human interference. 



Reproductive powers of a similar kind are exhi- 

 bited very extensively in the lower departments of 

 the animal kingdom. The Hydra, or fresh water 

 polype, is capable of indefinite multiplication by 

 simple division : thus, if it be cut asunder trans- 

 versely, the part containing the head soon supplies 

 itself with a tail ; and the detached tail soon shoots 

 forth a new head, with a new set of tentacula. If 

 divided longitudinally, each half will, in the course 

 of an hour, have formed itself into a separate tube 

 by the folding in and adhesion of the cut edges, and 

 will employ its tentacula in laying hold of objects. 

 Even if divided into several strips, each fragment 

 becomes a new tube, not, however, as before, by 

 the folding in of its edges, but by the formation of 

 a new cavity within its substance. If any of the 

 tentacula, or any portion of one of them, be cut off, 

 the mutilation is soon repaired ; and if the whole 

 animal be divided into a great number of pieces, 

 each fragment acquires, in a short time, all the 

 parts which are wanting to render it a complete 

 individual. The same phenomena are observed, 

 and nearly to the same extent, in the Planaria. 



orange tree, when planted in a favourable soil, sends down roots, and 

 is capable of giving origin to an entire tree. According to the ob- 

 servations of Mirandola, the leaf of the Bryophyllum, when simply 

 laid on moibt ground, strikes out roots, which quickly penetrate into 

 the soil. (De Candolle, Physiologic Vegetale, ii. 677.) The leaves 

 of the monocotyledonous plants often present the same phenomenon. 



