250 ELEMENTS OF BIOLOGY 



mentally at certain stages of development (Fig. 171) and each por- 

 tion give rise to a normal form. It is extremely probable that 

 identical twins in mammals are the products of the division of a 

 single embryo at an early stage. 



Agamic reproduction by budding is a common but not universal 

 property among plants. The usual method of artificial propagation 

 of many plants is by the separation and proper handling of a bud or 

 cutting. In Nature it is most strikingly illustrated by creeping stems 



Fig. 172. — A strawberry plant and its daughter plants agannically produced. Com- 

 pare as to general character with agamic reproduction in animals as illustrated in 

 Fig. 170. (After Child: Senescence and Rejuvenescence, published by the University 

 of Chicago Press.) 



that develop independent root and shoot systems and become sep- 

 arate plants, for example, the strawberry runner (Fig. 172). The 

 common potato is an underground stem in which is stored large 

 quantities of starch and other materials and on which are developed 

 latent buds known as eyes. Under suitable conditions these buds 

 give rise to root and shoot systems. This modified stem is the chief 

 method of propagation and is obviously an organ for agamic 

 reproduction. 



Gametic Reproduction. Gametic reproduction is effected by 

 the development of a new individual from a single cell, the zygote, 



