32-2 



THE aG^ICULTDRAL NEWS. 



OCTOBEK IS, 1919. 



I'ndcr conditions of fli'ought' the impermeable 

 hypodfi-.nia or skin of the root approaches closer and 

 ■cl"...syr t<) the tip, until if dryness is severe enough, it 

 rejiches the root-cap. Thus the roots can automatically 

 check the ab.sorption of water without dying. The 

 roots under ordinary conditions will absorb salt solu- 

 tions up to considerable concentratiuii-j, but their 

 structure renders them safe against concentrations 

 that arc }ii>ch enough to b^' toxic. 



The auiount of water that can be absorbed by the 

 coco-nut is relatively great, and transpiration in 

 sunlight is very rapid. It is interesting to note here 

 that recent investigations in England have shown 

 that surprisingly high transpirations are characteristic 

 of many halophytes. It ha.s also been shown that red 

 and purple leaves transpire more rapidly than green 

 leaves. This is of particular interest in view of the 

 various opinions that have been put forward with 

 regard to the physiological role of anthocyan (red 

 •colouring matter) of plants. It will be remembered 

 that the young leaves of the Seaside Grape (Coecoloba 

 uvife'i'a), a typical West Indian halophyte, aie nearly 

 always red or yellow. 



Returning to the ijuestion of sali-sohuion in the 

 soil, it has been indicated that the roots of the coco- 

 mtit, according ti C'opeland, proteofc themselves against 

 high concentrations by rneuns of the growth of the 

 hypodermis. Now in most halophytes the arrange- 

 ment is entirely different. According to Hill, (') 

 true halophytes, which rc(juire common salt 

 ior successful gi-owth, can adapt themselves 

 to alterations in concentration otberwirie. This 

 is effected by the root- hairs which can accoiniuodate 

 their internal osmotic pressure as the sidinity of the 

 Boil-water falls in concentration, and convei-siily, the 

 toot-hairs can r.aise their osmotic strength as the 

 {salinity of the surrounding soil-water increis<!3.* 

 [Phis result is of fundatneiital imp<jrtance. It explains 

 the reason how halophytes exist under constantly 

 changing saline conditions. It shows thai plants 

 vhich arc devoid of this capability laiisi sufler and 

 eventually die otit under saline conditions. 



The question now arises as to whet.her sugar-cahe 

 or cotton is adapted in any way phyiiiologically t« 

 withstand .ilterations in the salinity of soil-solution. 

 According lo Harrison (■') the soil water m the fertile 



. ♦ ( hiniOHis in the interoliiinge of two fluids «J ditfereat 

 dt-nttitUs wlifii aejKirated lij- a porous iiil-iii1>i'iii)i;. In tho ca^c 

 of r<)< 't ■ liair.'', osiiiosiB takes place ln;t,wi!<;n tlirf dOliap, and soil- 

 si.lutioii tlii'iiouli Oil' pcpiiis inciiilir.»iic»- cf tl" oytoplasm of 

 tl.. c-ll. 



parts of tho E.^cp^rimeatal Fields at the Kotaiiic 

 <Iardens, British (iuiana, contains in one acre, to a 

 depth ot 12 feet from the surface, about 43 tons of 

 .sodium chloride (common salt), as well as considrrvb'e 

 but much smaller quantities of other salts. 



In this connexion Harrison states: ' The marked 

 aikalmity and t,he high content of salts of magnesium 

 and sodium chloride of the ascending sul)soil v.ater 

 act detrimentally on growing crops during dry seasons, 

 and may be the cause of much of the cessation of 

 active growth, of the wilting and of the scorching of 

 crops soon after the commencement of and during the 

 dry season." 



On the authority of Maxwell, it is stated that in 

 ordinary soils a percentage of sodium carbonate ex- 

 ceeding O'l 5 percent will prevent a normal growth of 

 cane. In Porto Kico, Zerban ( ' ) has found a combina- 

 tion of bicarbonic acid and chloride up to 04 per cent, 

 harmless. It appears that cane in its later stages 

 of growth may stand a much higher quantity of salt 

 without visible injury. It may be noted that an 

 occasional Hooding with sea-water on many West 

 Indian cane fields has been found actually beneficial; 

 but, according to Prinsen Geerligs, this is due to the 

 chemical effects on the soil rather than to any 

 physiological action upon the cane itself. 



As in the case of bicarbonic acid, the presence 

 tjf nitrogen and calcium lessen.^ the toxic action of 

 common salt. 



It is clear from Zerban's work in Porto Rico* 

 that salt when present ahme in large quantities (say 

 2 per cent.) greatly lowers the yield of c;ine, and as 

 well, has a most deleterious effect upon the composi- 

 tion of the juice. 



Nevertheless it would appear that while 

 chlorides are inimical to the growth of the sugar-cane, 

 this plant can to .some consider.able extent adapb 

 itself to grow in the presence of appreciable ci>ncen- 

 trations. Jso information is available concerning the 

 physiological action of the root of this plant such as 

 has been recorded with regard to the coco-nut and the 

 true halophytes. 



The facts given in regard to Mritish (iuiana 

 point to thi! f.ict that silinity may ari.se from tho 

 subsoil as well as from high tides ami storms- -a point 

 which Cop(!lii.nd appears to o»'erl()ok in regard to tho 

 adaptability of the coco-nut- 



* Zerljaij's iigunw are i xpii:.s~iMi in purr.c.diji'^es anil 

 IlariiHon'i; in bma jioraci-u, su thi»l oinipiiris'Jij is ilittii.-ult. 



