Environment and Adaptation 203 



be an abundance of moisture, these plants take up 

 a relatively small amount, as the excess of salt dis- 

 solved in the water is not favorable for their 

 growth. Hence these plants show the fleshy habit 

 characteristic of xerophytes. Plants growing along 

 the seashore often show this same fleshy texture. 

 Examples of these strand plants are the ice-plants 

 (Mesembryanthemum), sand verbena (Abronia), 

 and sea-rocket (Cakile). 



LIGHT 



Modifications Associated with Photosynthesis 



As photosynthesis is the most important of the nu- 

 tritive processes of the plant, it is not surprising 

 that some of the most striking modifications of the 

 plant-body are obviously associated with chloro- 

 phyll work. In the cells of all of the algae there 

 are present definite organized structures, chromato- 

 phores, which are the essential photosynthetic or- 

 gans, and the form and position of these is to a 

 great extent correlated with the direction and 

 the intensity of the light rays. In the lowest forms 

 there is usually a single large chromatophore which 

 may assume a very complicated form, as in some of 

 the pond-scums (Spirogyra) or the desmids; or 

 there may be two or more large chromatophores, 

 which are often more or less divided, possibly a con- 

 trivance for increasing their efficiency. Only a 

 relatively small number of the green algae, e.g., 



