580 THE REPRODUCTIVE FUNCTIONS. 



facts, which are well known to agriculturalists, 

 exhibit only the capabilities of vegetative power 

 under circumstances which do not occur in the 

 natural course of things, but have been the eftect 

 of human interference. 



Reproductive powers of a similar kind are 

 exhibited very extensively in the lower depart- 

 ments of the animal kingdom. The Hydra, or 

 fresh water polype, is capable of indefinite mul- 

 tiplication by simple division : thus, if*it be cut 

 asunder transversely, 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 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. 

 The Asterias, the Actinia, and some of the lower 

 species of Annelida, as the ISais, are also capable 



nourishment. It has been found that when these conditions are 

 present, even the leaf of an orange tree, when planted in a fa- 

 vourable soil, sends down roots, and is capable of giving origin 

 to an entire tree. According to the observations of Mirandola, 

 the leaf of the Bryophyllum, when simply laid on moist ground, 

 strikes out roots, which quickly penetrate into the soil. (De 

 CandoUe, Physiologic Vegetale, ii. 677.) The leaves of the mo- 

 nocotyledonous plants often present the ime phenomenon. 



