Ecologic Study of Living Organisms 637 



When the latter are stimulated by an insect, the two halves of the leaf 

 fold quickly together. The soft parts of the insect are actually digested 

 by digestive juices secreted by the glandlike hairs on the leaf. In the 

 sundews the flat leaf is covered with long, radiating, glandular hairs 

 covered at their tips with a sticky secretion which contains a digestive 

 enzyme capable of digesting insects lighting on the hairs. In the pitcher 

 plants the leaves form urnlike pitchers which are partly filled with liquid 

 in which the insects are captured and digested. 



The bladderwort is a rootless, submerged water plant which bears 

 numerous small bladderlike structures on its branches. Each bladder 

 has one opening to the outside, closed by a valvelike trap opening in- 

 ward. Small aquatic animals entering these traps are prevented from 

 escaping and are used as food. In all these cases of predacious plants 

 the ecologic distribution of the captured animals is affected. 



(i) Plants Affording Shelter, Protection, and Concealment for Ani- 

 mals: Many animals live in certain places because they receive pro- 

 tection and shelter from particular plants. Without these plants they 

 would be subjected to the ravages of nature and would be exterminated, 

 or at least be distributed elsewhere. A little investigation will reveal 

 many instances where animals are distributed in certain areas because 

 of the presence of plants. Where do we find more animals, in a sandy 

 area with limited vegetation or in an area with abundant plant life? 

 List as many reasons as you possibly can for this phenomenon. 



4. Human Factors. — 



(a) Animal and Plant Quarantine Regulations: Quarantine regula- 

 tions enforced by the government prevent, to a great extent, the import- 

 ing of many varieties of animals and plants which otherwise would be 

 brought to us from foreign countries in large numbers. Many of these 

 types, if imported, would be very destructive of plants and other ani- 

 mals. In addition, these unwelcome immigrants would upset the natural 

 balance or equilibrium of the present flora and fauna. This change in 

 the equilibrium would necessarily affect the ecologic relationships of 

 many other types of living organisms either directly or indirectly. In 

 spite of this vigilance, many undesirable animals and plants are im- 

 ported either secretly or knowingly. It is suggested that the organisms 

 responsible for the destruction of large numbers of our elm trees (Ameri- 

 can elm disease) were brought in from Europe. If this parasite could 

 have been prevented from entering, we could have saved many of our 



