SEXUAL AND ASEXUAL REPRODUCTION 243 



evidently spores, but they arise from the division of a mass 

 resulting from the fusion of two reproductive cells; and to 

 distinguish them from other spores they are called sporozoites. 

 By comparing this history with that of the malarian Plasmo- 

 dium, it will be evident that the spores of the latter, which are 

 formed in the body of the mosquito, must be sporozoites, since, 

 like those just described, they arise from the breaking up of 

 the mass of the two cells which have united by cell union. 

 Monocystis as here described shows no spores which correspond 

 to those that appear in the human blood; Fig. 25 g and h. 



REPRODUCTION IN MULTICELLULAR ORGANISMS 



Multicellular organisms have the same two general types of 

 reproduction as found in the unicellular; namely, simple divi- 

 sion, and division accompanied by cell union. 



DIVISION WITHOUT CELL UNION 



Multiplication by Simple Division. Simple division among 

 multicellular organisms is more common among plants than 

 among animals; and excellent examples of it are familiar to all. 

 Many of the lower plants, like liverworts, multiply by the for- 

 mation of buds called gemmae, which break away from the 

 original, and form new plants. Even among the higher plants 

 the same general method is found. If one of the branches of 

 a weeping-willow tree is broken off and stuck into moist ground, 

 it will take root and grow into a new tree. Indeed, we can 

 cut the branches of a willow into practically as many pieces 

 as we wish, and find each one is capable of taking root and 

 growing into a new tree. The same thing is true of most ordi- 

 nary plants, for, with a few exceptions, trees and smaller plants 

 may be reproduced indefinitely by breaking off their branches 

 and putting them into the proper conditions for taking root. 

 While a few plants fail to show this power, it is a character 

 found very commonly in the vegetable kingdom. Many plants 

 normally multiply upon a similar principle. The strawberry 



