THE AMERICAN BOTANIST 



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vides in growth, it forms two distinct individuals. When the 

 organism consists of many ceUs, division may resuh merely 

 in growth, but if one or more of the new cells produced become 

 separated from the original colony and form new individuals ; 

 this is reproduction and the beginning cell is a spore. In 

 higher plants, a union of cells may precede division. This is 

 what happens in flowering plants when one of the sperms pro- 

 duced in the pollen tube unites with the egg cell in the young 

 ovule in the production of a seedling by subsequent cell divis- 

 ion. So long as conditions are favorable, the divisions that 

 merely result in growth proceed rapidly, but when unfavorable 

 conditions arise, the protoplasm especially in one-celled forms, 

 shows a disposition to draw together into a roundish mass and 

 to cease dividing until better days come. Such bits of proto- 

 plasm known as spores serve to distribute the species, as well 

 as to tide them over unfavorable seasons. For this reason, 

 probably, flowering plants are inclined to bloom whenever any- 

 thing occurs to threaten their continued growth. 



Water Lily Aphid on Plum. — Nature usually arranges 

 matters so that there is always sufficient plant pests to go 

 around. Pond lilies, water lilies, and other aquatic vegetation 

 are protected from many enemies by the medium in which they 

 live, but even in the water they do not entirely escape the plant 

 lice or aphids. There is one species that preys on the water 

 lily, cat tail, and water plantain, wdiich seems particularly de- 

 signed to bother water vegetation, being equipped with w^axy 

 areas which prevent it from getting w^et if it happens to fall in 

 while feeding on aquatic plants. The interesting thing about 

 this aphid, however, is the fact that it also feeds on the plum, 

 being one of the most destructive of the insects that bother that 

 tree. It is a migratory species living on the plum until hot 

 weather comes and then going to its home at the lakes until 

 the temperature moderates. Then back it goes to the plum 

 where it deposits the eggs which last through the winter and 

 hatch out new colonies the following spring. 



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