119 



Water assists the feeding of the plant in supplying it with the two 

 elfnients of whith it is composfd, viz. : hydrogen and oxy^/en, which 

 are necessary for the huildirg up (f certain carbon compounds such as 

 starch and sugar, and secondly in acting as a vehic'e by which the 

 other foims- of plant food are distribiited through(ut the plant. The 

 importance of the wxrk done by water in the second place will be 

 realised if it is remembered that w ith the exception of 1 he carbonic 

 acid gas passing in from the air through the leaves, all the substances 

 that go to build up the plant enter it thrc)Ugh the roots. Further 

 nothing can pass in through the roots that is not in solution and in 

 fact in a very dilute solution. It fellows then that the plant is 

 deperdent upon the water in the soil for the wIk le of its food ccnsti- 

 tuents except carbon. 



Yeiy few soils are ? o poor in available plant fo( d that they cannot 

 support plant life if ihey have a sufficient water supply. Hint surely 

 justifie sus in considering that the conservation of soil moisture should 

 jeceive the utmost attention from the planter. 



The nec( ssity for moisture sj rings up simultaneously with the actual 

 birth of the plart. For the very first process in the plant's life 

 history, the change from the dormant to the living state, which is 

 < ailed gej miration — can only take place if the seed is supplied with 

 water. As the seed ripens it parts with almcst the whole of its water 

 thereby rendering the protoplasm of the ir dividual cells inactive. For 

 this ccmplex substance, giving to every cell of the phmt what we know 

 ts 'life,' can exhibit none of its vital activities in the absence of a 

 constant supply of water. Thi^ explains why the seed is able to lie 

 doimant until it obtains sufficient moisture to re-awaken the slumber- 

 ing protoplasm. The next thirg the \^ ater has to do for the plant is 

 1o dissolve the food stored up in the seed and bring it into a condition 

 suited to the requirements of theyouDg plant or embryo. It is, too, the 

 absorption of water thut causes the seed to swell up and bur^-t its case, 

 thereby allowing the young plant to make its way out. As soon as the 

 food store has been consumed, the young plant has to commence ab- 

 sorbing its food in a crude form from the soil. Water then has to 

 dissolve from the soil salts containing the following elements : — nitro- 

 gen, sulphur, phosphorus, calcium, potassium, magnesium and iron. 

 The other elements required by the plant for food are hydrogen, oxy- 

 gen and carbon, of these the ctirbon is obtained, as has been mentioned, 

 from the carbonic acid gas of the air, while the other two are got by 

 splitting up the w^ater itself into its two component elements. Ihus 

 with the aid of water the leaves receive a sup| ly oi all these elements 

 and manufacture them up into the complex organic substances of which 

 the plant is composed. Ihis passage of water up from the roots to the 

 leaves may be seen by placing a young plantlet whose roots have been 

 freed from soil in a saucer of water dyed blue with aniline. After 

 Eome time the veins of the leaves will be found to be stained. 



Of this large amount of w^ater that passes up into the leaves only a 

 comparatively small proportion is actually required as food, the bulk 

 of it beirg got rid of by the process of trmispiradon. 



The solution which passes in through the plant root must be very 

 dilute, ^'ome idea of the weakness of this solution will be obtained by 

 bearing in mind what has already been sai l about the large proportion 



