loo POPULAR SCIENCE MONTHLY. 



other is a dwarf and unproductive. Below ground tlie conditions 

 are many, and all subject to infinite variation. Thus, the soil may 

 be deep or shallow, the particles small or large, the moisture abun- 

 dant or scant, and the food elements close at hand or far to seek — 

 all of which will have a marked influence upon the root system, its 

 size, and form. 



Coming to the aerial portion, there are all the factors of 

 weather and climate to work singly or in union to affect the above- 

 ground structure of the plant. Temperature varies through wide 

 ranges of heat and cold, scorching and freezing; while humidity or 

 aridity, sunsliine or cloudiness, prevailing winds or sudden tornadoes 

 all have an influence in shaping the structure, developing the part, 

 and fashioning the details of form of the aerial portions. Phyto- 

 ecology deals with all these, and includes the consideration of that 

 struggle for life that plants are constantly waging, for environ- 

 ment determines that the forms best suited to a given set of condi- 

 tions will survive. This struggle has been going on since the 

 vegetable life of the earth began, and as a result certain prevail- 

 ing conditions have brought about groups of plants found as a rule 

 only where these conditions prevail. As water is a leading factor 

 in plant growth, a classification is made upon this basis into the 

 plants of the arid regions called xerophytes. The opposite to 

 desert vegetation is that of the fresh ponds and lakes, called hydro- 

 phytes. A third group, the halophytes, includes the vegetation of 

 sea or land where there is an excess of various saline substances, 

 the common salt being the leading one. The last group is the 

 mesophytes, which include plants growing in conditions without 

 the extremes accorded to the other three groups. 



This somewhat general classification of the conditions of the 

 environment lends much of interest to that form of field botany 

 now under consideration. As the grouping is made chiefly upon 

 the aqueous conditions, it is fair to assume that plants are espe- 

 cially modified to accommodate themselves to this compound. 

 Plants, for example, unless they are aquatics, need to use large 

 quantities of water to carry on the vital functions. Thus the salts 

 from the soil need to rise dissolved in the crude sap to the leaves, 

 and in order that a sufficient current be kept up there is transpira- 

 tion going on from all thin or soft exposed parts. The leaves are 

 the chief organs where aqueous vapor is being given off, sometimes 

 to the extent of tons of water upon an acre of area in a single day. 

 This evaporation being largely surface action, it is possible for the 

 plant to check this by reducing the surface, and the leaf is coiled 

 or folded. Other plants have through the ages become adapted 

 to the destructive actions of drought and a dry, hot atmosphere, and 



