248 ECOLOGY 



as to make them appear cylindrical — an arrangement 

 for protecting the stomata (Fig. 98) and preventing tran- 

 spiration. All these, it will be observed, are xerophyte 

 characteristics, and the object in both cases is the same 

 — economy of moisture. The reason why such adapta- 

 tions are necessary in halophyte plants is because the 

 mixture of salt in the water of the soil increases its 

 density so that it is difficult for the plant to absorb what 

 it needs (Sec. 227). Hence, halophytes are in the con- 

 dition of Coleridge's "Ancient Mariner''; with "water, 

 water everywhere," they are practically living under 

 xerophyte conditions. 



PRACTICAL QUESTIONS 



1. Why do florists always cultivate cactus plants in poor soil? 



(350-) 



2. What would be the effect of copious watering and fertilizing on 

 such a plant? (350.) 



3. Why must an asparagus bed be sprinkled occasionally with salt? 

 (348, 354-) 



4. If a gardener wished to develop or increase a fleshy habit in a 

 plant, to what conditions of soil and moisture would he subject it? 



(350. 3S4-) 



5. What difference do you notice between blackberries and dew- 

 berries grown by the water and on a dry hillside? 



6. Is there a corresponding difference between the root, stem, or 

 leaves of plants growing in the two situations, and if so account for it? 



7. When a tract of dry land is permanently overflowed by the 

 building of a dam or levee, why does all the original vegetation die, or 

 take on a very sickly appearance? (349.) 



8. Should plants with densely hairy leaves be given much water, 

 as a general thing? (354-) 



9. A farmer planted a grove of pecan trees on a high, dry hilltop ; 

 had he paid much attention to ecology ? 



10. Give a reason for your answer. 



FIELD WORK 



Ecology offers the most attractive subject for field work of all the 

 departments of botany. It can be studied anywhere that a blade of 

 vegetation is to be found. In riding along the railroad there is an 

 endless fascination in watching the different plant societies succeed one 



