SHOOTS 



57 



the protected stem. Tins position is also talien advantage 

 of for comparatively safe food storage, and such stems are 

 apt to become more or less thickened and distorted liy this 

 food deposit. 



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

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

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

 directions, and l)ecome interwoven into 

 a mat or carpet. They are found 

 especially on sterile and exjjosed soil, 



Flu. 47. A strawbt'iT}' jilaiit, showiiiL' ;] runner which hiis ilevel- 

 oped a new l)Uint, wliich in turn liay sent out anotlier run- 

 ner. — After Sei'bkrt. 



and there may be a,n intport;int relation Ijctween this fact and 

 their habit, as there may not he sutficient building material 

 for erect stems, and the erect i^osition might result in too 

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

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

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

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

 stand upright are not necessary. On the other h;md, such 

 a stem loses in its ])ower to display leaves. Instead of 

 Ijeiu"- free to put out its leaves in every direction, one side 

 is ao-ainst 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. is). 



We mav 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 



