SHOOTS 



57 



the protected stem. This position is also taken advantage 

 of for comparatively safe food storage, and sucli steins are 

 apt to become more or less thickened and distorted by this 

 food deposit. 



44. The procumbent type. — In this case the main body 

 of the stem lies more or less prostrate, although the advanc- 

 ing tip is usually erect. Such stems may spread in all 



directions, and become interwoven into 

 mat or carpet. They are found 



especially on sterile and exposed soil. 



Fig. 47. A strawberry plant, showing a runner which has devel- 

 oped a new plant, which in turn has sent out another run- 

 ner.— After Seubert. 



and there may be an important relation between this fact and 

 their habit, as there may not be sufficient building material 

 for erect stems, and the erect position might result in too 

 much exposure to light, or heat, or wind, etc. Whatever 

 may be the cause of the procumbent habit, it has its advan- 

 tages. As compared with the erect stem, there is economy 

 of building material, for the rigid structures to enable it to 

 stand upright are not necessary. On the other hand, such 

 a stem loses in its power to display leaves. Instead of 

 being free to put out its leaves in every direction, one side 

 is against the ground, and the space for leaves is diminished 

 at least one-half. All the leaves it bears are necessarily 

 directed towards the free side (see Fig. 18). 



We may be sure, however, that any disadvantage com- 

 ing from this unfavorable position for leaf display is over- 

 balanced by advantages in other respects. The position is 



