222 REPRODUCTION IN PLANTS AND ANIMALS 



Food 



growth. New living organisms, however, are usually formed by 

 other methods. If two cells, from two plants or animals of 

 different sexes, come together to form a new individual we call this 

 a case of sexual reproduction. But if the new organism is formed 

 by a cell or cells separating from a single parent to form a new in- 

 dividual this is said to be asexual reproduction. 



Asexual Spores. — Asexual reproduction is usually by means of 

 the formation of asexual spores. An example of this kind of spore 



formation is seen in the black mold 

 of our homes. If a piece of moist 

 bread is exposed to the air in the 

 schoolroom for a few minutes, 

 then covered and kept in a warm 

 place, in a day or two a fuzzy 

 whitish growth will appear on the 

 surface of the bread. This growth 

 shortly turns black. If we now 

 examine a little piece of the bread 

 with a lens or low-powered micro- 

 scope, we find a tangled mass of 

 threads (the myce'lium) covering 

 its surface. From this mass of 

 threads project tiny upright stalks 

 bearing round black bodies, the 

 sporan'gia or fruiting bodies. 

 Little rootlike structures known 

 as rhi'zoids dip down into the 

 bread, and absorb food. The 

 sporangia contain many tiny 

 bodies called spores which have 

 been formed by the division of the 

 protoplasm into many separate 

 cells. When grown under favor- 

 able conditions, the spores will produce more mycelia, which in 

 turn bear sporangia. 



Yeasts are another kind of plants that form asexual spores. 

 The yeast plant is microscopic in size. It lives in sugary solu- 

 tions, such as fruit juices, and multiplies rapidly by an asexual 



Sporangium 



Hyphs 



Rhizoids 



Mold reproduces by means of asexual 

 spores. 



