370 



RELATION TO ENVIRONMENT. 



jects high enough to climb upon. In the prostrate type, there 

 is economy in stem building. The plants depend on the ground 

 for support, and it is not necessary to build strong, woody trunks 

 for the display of the foliage which would be necessary in the 

 case of an erect plant with a foliage area as great as some of the 



Fig. 424- 

 Prostrate type of the water fern (marsilia). 



prostrate stems. This gain is offset, at least to a great extent, 

 by the loss in ability to display a great amount of foliage, which 

 can be done only on the upper side of the stem. 



Other advantages gained by the prostrate stems are protec- 

 tion from wind, from cold in the more rigorous climates, and 

 some propagate themselves by taking root here and there, as in 

 certain roses, the strawberry plant, etc. Some plants have 

 erect stems, and then send out runners below which take root 

 and aid the plant in spreading and multiplying its numbers. 

 . 720. The decumbent type. In this type the stem is first erect, 

 but later bends down in the form of an arch, and strikes root 

 where the tip touches the ground. Some of the raspberries 

 and blackberries are of this type. 



