IRISH GARDI.NING 



101 



IK- 



klllt 



ami Water. 



Hv I'.. t>. Sin i;i; \i;i>. 



Wl I I li-TI' waK'i- lluTc i-an bo no lilo. 

 \11 li\ln|^- lliiiii^-s, wlicllu-r plaiils or 

 animals, conlain in their cells a certain 

 anionnl ol water, and if this be reinoxed 

 ileath ensnes. In the case of plants ihe 

 anionnl of water nccessarv to support Hie 

 \arles willi tlic species o( plant and with llie 

 stale of i^rowth or rest in which il happens 

 t o b e . A 

 lichen or moss 

 s^frowini^' on a 

 rock retjuires 

 very little 

 water c o m - 

 pared with a 

 soft plant like 

 rhnbarh, and 

 the Liuantily 

 o( water con- 

 tained in a 

 reslini;' seed 

 or spore is 

 \ er\" s m a 1 1 

 c o m p a V e d 

 w i t h that 

 \\ hich the re- 

 sultant plant 

 will contain 

 w h e n i n a 

 Stat e o f 

 i^- r o w t h . 

 Water makes 

 up about 50 



per cent, of the wei_t;ht of a wood\- stem, 70 per 

 cent, to 80 per cent, of theweiijht of herbaceous 

 plants, while in the case of succulent plants and 

 fruits it amounts to as much as 85 per cent, to 

 95 per cent, of their total weight. 



Seeing then that the body of the higlier plants 

 is composed so largely of water it must be o( 

 great physiological importance to them. If the 

 growing stem of a herbaceous plant be cut anil 

 allowed to remain in the sun for a short time it 

 will become limp and soft, and will no longer 

 assume an upright position when helil in tlie 

 hand. When placed in water it again becomes 

 rigid. Consequently the rigidity and firmness 

 o( non-woody plants depends on the water con- 

 tained in the cells— in fact the cells of a growing 



plant are ilistended with w.itcr just as a bicycle 

 tyre is with air. 



Water is also used ilirectly by plants in llu- 

 making of their food — starch, sugars, itc. In 

 or(.ler to form roo'frammes of starch 55 grammes 

 of w.iter are nece.ssiiry, and to make the .same 

 quantitx of glucose 60 grammes of water must 

 be used. Then when the food is made it has to 

 be carried to the different parts of the plant, and 

 it can onlv travel throug'h Ihe cells and vessels 

 when dissoKeil in water. 



\o solid substance can enter a plant, con- 



sequently 



ill 



Sii.KM-; 



the raw ma- 

 terials in the 

 soil from 

 which a plant 

 forms its food 

 must be taken 

 up, dissolved 

 in the soil 

 water a n il 

 carried to the 

 leaves by the 

 " trail s p i r a - 

 tion " current. 

 This \]ow of 

 water from 

 the roots to 

 the leaves is 

 ot f u n d a - 

 mental i m - 

 portance t o 

 the nutrition 

 of the plant. 

 >iiKi HI 'I' h e water, 



containing a 

 very small percentage of dissolved salts, enters 

 by the root hairs or by the general .surface of 

 the root, and travels upwards through the vessels 

 of the wood}- part of the stem, or in a herbaceous 

 stem through the wood vessels of the vascular 

 strands. Thence it passes into the veins of the 

 leaf, and is evaporated or transpiied away 

 through the stomata or minute pores 

 which are scattered in enormous numbers 

 over the lower surfaces of the leaves. Tlie 

 salts dissolved in the w^ater are left behind in 

 the leaf, and, of course, the plant retains 

 what water is necessary for food manufacture 

 and for the turgidity of the cells. Since the 

 soil w-ater contains but a very weak solution 

 of salts (phosphates, nitrates, and salts ot 



