418 



THE AGRICULTURAL NEWS. 



Decembee 30, 1916. 



Briggs and Shantzf, who have carried out a large 

 amount, of work in transpiration in the United 

 States, employing such plants as millets, Indian corn, 

 and sorghums, find that transpiration per unit area of 

 plant surface shows less variation than the transpira- 

 tion per unit weight of dry matter. In other words, 

 the greater efficiency shown by certain plants 

 in the use of water appears to be due more 

 to a reduction in plant surface than to a reduction in 

 transpiration per unit area of surface. 



If this is generally true, we may assume that 

 a resistant cane plant, for example, in time of drought, 

 protects itself by reducing its leaf surface, while at the 

 same time it maintains carbon assimilation at some- 

 thing approaching the normal extent. A variety 

 which is susceptible to drought might not be able to 

 adjust itself in this manner. 



The same workers have shown that the natural 

 tendency to transpire, quite apart from conditions of 

 enrironment, increases with some crops e.\-ponentialiy 

 during the early stages of growth. Sudan grass, for 

 •e.xample, doubles its 'transpiration tendency' every four 

 days during the early growth period. This is rather 

 surprising, since as every plant grows older it is 

 anatomically better able to control transpiration on 

 account of the thickening of the cuticle and other 

 changes of a similar nature. 



From a' practical stand-point a considerable amount 

 of light is thrown upon the problem of water loss 

 from plants by the American work* having regard to 

 the relationship between leaf-area and extent of root 

 system in Indian corn and Sorghums. 



According to these operations, secondary roots of 

 Sorghum plants as compared with those of corn are 

 twice as numerous per unit of primary roots. The leaf 

 area of the corn plant at all stages of its growth is found 

 to be approximately twice as great as that of Dwarf 

 Milo luai/.e, and never less than 1'5 times that of Black- 

 hull Kafir corn. The Sorghums, therefore, should have 

 the advantage over the corn plant under any climatic 

 condition tending to bring' about a loss of water from 

 the plants. The two kinds of Sorghums as compared 

 with the corn plant had only one-half the leaf surfcice 

 exposed for the evaporation of water, and also a root 

 system which, judging irom the number of secondary 

 roots, would be twice as efficient in the absorption of 

 soil moisture. 



hfoufual of Aqricultwal Ruearch, Vol. VII, No. 4. 

 lE.'-peum-iit Stativn Record, Vol. 3.5, No. 5. 



There is probably some connexion between the 

 relation in the extent of leaf-area and root system which 

 may help to explain drought resistance in varieties of 

 sugar-cane, and the question arises; do drought-resistant 

 varieties have large root systems and small leaf-areas ? 

 It is not an easily arranged matter to study the root 

 system of a plant like the sugar-cane, but efforts to do 

 so would probably be well worth while. Presumably 

 extent of root system, at any rate in a horizontal direc- 

 tion, must vary with the number of canes to the stool, 

 for the greater the number of canes the larger the under 

 ground stem and, therefore, the larger the root-producing 

 surface. It is well to remember that a variety of 

 sugar-cane having an extensive root system will, other 

 things being etiual, make greater demands upon the 

 moisture in the surface soil than a variety w-hose root 

 system is smaller. But as is known to be the case 

 with Sorghum, variation in leaf-area will decide to what 

 extent the plant uses its water efficiently. 



The sugar-cane in respect of its ability to thrive 

 under extreme conditions of environment is perhaps 

 the most remarkable plant under cultivation in the 

 tropics. This can be well appreciated by comparing 

 the limitations of cacao, rubber, limes, and cotton, all 

 of which require very special conditions of environment. 

 One reason why the sugar-cane can tolerate relatively 

 dry, as well as relatively wet, conditions may be on 

 account of the juice stored up in the stem. It may be 

 that tb.e plant carries on over periods of dry weather 

 by drawing upon these reserves of moisture. It is 

 somewhat significant that the variety B.147, which when 

 well established, is a vigorous grower in dry localities, 

 possesses an exceptionally high percentage of juice 

 only moderately rich in sucrose; whereas B. 208, which is 

 susceptible to drought, yields only a moderate ipian- 

 tity of juice which is, however, exceptionally .rich in 

 sucrose. 



DEPARTMENT NEWS. 



Mr. W. R, i>iiiiliip, Scientific Assistant, Imperial 

 Department of Agriculture, left Barbados on December 

 23 by the S. S.' Crown of Cordova" with the object of 

 paying a visit to Triniilad. It is expected that 

 Mr. Dunlop will return by the C.K.IM.S. 'Chignecto' 

 on .January 10. 



Observations relating to the staple crop in St. Lucia 

 during November 1!)16 indicate that the crop i.s difficult to 

 gauge. Certain localities appear to have sutfered from 

 excessive rain.s and other localitiea increased their crop. The 

 result will probably be a fairly normal crop. The 

 lime crop is again coming in. The extension of area under 

 limes has practically finished for the present year. The stand 

 of sugar-cane throughout the isUnd was very promising. 



