generation may even be, so far as we know, quite absent. 

 Coupled with the asexual reproduction represented in the 

 alternation of generations there is another type of asexual 

 reproduction through the formation by budding from the 

 original unit (phyton) of vast numbers of additional units 

 resulting in the creation of colonies, as in the flowering plants. 



For physiological reasons the formation of sexual products 

 by a plant is. a much more exhausting process than it is for an 

 animal, and furthermore, as plants are for the most part 

 terrestrial, all sorts of devices must be evolved and adopted to 

 guard against the dessication of the germ cells as well as to 

 insure the fertilization of the ova. The natural result of these 

 difficulties has been to reduce sexual reproduction in all plants 

 to a minimum and to increase asexual reproduction to a 

 maximum. 



In the animals there is no marked physiological disconti- 

 nuity between the formation of germ cells and the formation of 

 the other cells of which the body is composed. As most animal 

 types are marine, or if not marine are active, and their germ 

 cells have a specific gravity only slightly greater than that of the 

 medium in which they live or than their body fluids, there is no 

 necessity for special adaptations to insure fertilization or to 

 protect the embryos. On the other hand, the complex organi- 

 zation of a multicellular animal and the centralization and 

 coordination of its organs render asexual reproduction both 

 difficult and dangerous, and in the animals therefore sexual 

 reproduction is developed to a maximum while asexual reproduc- 

 tion and vegetative reduplication are reduced to a minimum. 



Asexual reproduction occurs in most coelenterates ; some, 

 like some sponges, reproduce by budding and fission, while 

 many by continuous budding from an original asexual indivi- 

 dual form extensive colonies in which the units are usually 

 differentiated and specialized for various functions. Though 

 they are entirely different in every detail of structure, just as 

 we see in the sponges a reflection of the thallophytic method of 

 mass increase so we recognize in the colonial coelenterates, 

 especially in such types as the hydroids, a close parallel to the 

 phanerogams, the colonies, dendritic or otherwise plant-like in 

 form, being composed of more or less differentiated reduplica- 

 tions of an original asexual individual relatively few of which 



