178 BOTANY: PRINCIPLES AND PROBLEMS 



489. From its structure, whicli of the tissues of the phint do you think 

 might serve most readily as a moans of transmitting stiumU quickly 

 from one part of the plant to anotlier, in somewhat the same way as do 

 the nerves among animals? 



490. Is there anything in the plant corresiDonding at all to the sense 

 organs of an animal? 



491. Give an example of an adaptation of a plant species to the 

 environment in which it lives. 



492. What danger may there be for a plant species in becoming very 

 closely adapted to a particular environment? 



493. Why are plants more susceptible to frost when water is abundant 

 in their tissues than when it is not? 



494. Rank, rapidly growing parts of plants are apt to be injured first 

 by frost. Wliy? 



495. Why is a slight frost in fall or spring often more disastrous to 

 plants than very much lower temperatures in the middle of the winter? 



496. Why wiH a warm period in midwinter often prevent a fruit tree 

 from bearing fruit the next season? 



497. It is better not to fertilize trees or shrubbery heavilj^ in the late 

 summer and fall. Why? 



498. A frost while fruit trees are just in bloom is more harmful than 

 it would be a little earlier or a little later. Why? 



499. Why do the first frosts of autumn usually come in low land? 



500. Wliy will an orchard of such fruit trees as the peach, which are 

 rather susceptible to cold, survive better if grown on a hilltop or on the 

 north slope of a hill? 



501. Which do you think will withstand frosts better, plants of salt 

 marshes or of ordinary soil? Why? 



502. Of what advantage and of what disadvantage is snow to 

 vegetation? 



503. Many of the higher animals can thrive and function normally 

 in the winter whereas the higher plants cannot. To what physiological 

 difference between the two groups is this due? 



504. Of what advantage is it to the plant to have its stems positively 

 phototropic and its roots negatively so? 



