HOW THK PI^\NT LIVES ll.'i 



uoiiiona, an<l oertaiu other couditiuiis to which 

 growth is seusitive. 



'2. The Factors of Growth 

 2<J. Water in thr plant 



184. The riijidity or stiffnoss of any lierb 

 or suceuk'Hl part is hirgely depoiuU'iit on its 

 water content. If a sueeulent branch is severed, 

 it soon loses its water by evaporation, and it 

 becomes flaccid, or wilte<l. Tiie proper exten- 

 sion, or tnrjLi^idity, of the cells of phiiits witii 

 water is necessary for active growtli. The j>as- 

 sage of the soil water into the plant, and there- 

 after its transfer from living cell to living cell, 

 is accomplished by the process of osmosis, which 

 is the dilTiisioii of liriuids thi'oiigh nienibi-aiics. 

 Much of this water eventually reaches certain 

 con(lucting parts, or bundles. 



185. Surrounding each rootlet for some dis- 

 tan<'e back of the tip is an enveloping growth of 

 delicate root-hairs. These hairs are single, 

 tubular cells, the outgrowth of single cells in 

 the outer layer of tlif root. Kach on«» contains 

 within its walls, as <lo all active cells, living 

 matter called protoplasm, along with cell-sap. 

 In the soil these delicate hairs push rea«lily in 

 amongst the soil particles, covering an immense 



