spore formation 



Coo 



THE YEAST PLANT 



The cells of this plant push out buds, which drop off at various stages, and continue 

 to grow and bud so long as food and other conditions are favorable. Under certain 

 conditions the protoplasm of a cell divides into two and then four parts, each of which 

 may remain inactive for an indefinite time. Such resting cells are called spores 



successive cell-divisions of the growing protoplasm, and they can dry up and 

 withstand conditions unsuited to growth for a long time. The malaria para- 

 site belongs to this class. The plasmodium, or ameba-like stage, of this species 

 is parasitic in red blood corpuscles. When it has grown as far as possible in a 

 corpuscle, the protoplasm divides into a large number of spores, which are 

 discharged into the blood plasma (see illustration, p. 622). 



Spores are so small, and they are produced in such tremendous quantities, 

 that they become widely scattered in the air. We can hardly find a sample 

 of dust that does not contain spores of several different species, including, of 

 course, bacteria. This accounts for the difficulty of keeping organic matter 

 from spoiling at ordinary temperatures in the presence of moisture. The 

 molds and mildews and yeasts and bacteria that spoil bread and other food, 

 cloth, leather, paper, damp hay, wood, and so on get started from such spores. 



In mosses we can see tiny puffs of spores come out of the graceful little 

 capsules at the tips of stiff bristles (see illustration, p. 412). On the backs of 

 fern fronds we can see the dark "fruiting bodies", which are masses of spore 

 capsules (see illustration, p. 387). The yellowish pollen which ardent fiower- 

 smellers get on their noses consists of tiny spores. And it is such flower spores, 

 scattered by the wind, that have brought certain species of plants into dis- 

 repute with many people because they are responsible for hay fever and asthma. 



W^e may think of these most widely scattered dust particles, produced in 

 inconceivably great numbers, as the resting stages in which species keep their 

 hold on life during the lean seasons. We may think of them as special means 

 for spreading out in space and so improving the chance of finding a favorable 



371 



