Vol. XVII. No. 422 



THE AGRICULTDKAL NEWb 



19.5 



some new, apparently more desirable strains, is not 

 without its danger. In the West Indies, for instance, 

 Mr. S. (". Harland states that recently in St. Vincent 

 a survey made of the forms belonging to the common 

 French bean (Phaseolus rulgarix) showed that, in'res- 

 pect of seed colour alone, twelve varieties existed in 

 that island, and it is certain that the number of kinds 

 differing in other characters must be many more. The 

 biological composition of no one species of cultivated 

 plant has yet been thoroughly investigated in the West 

 Indies, and it is highly desirable that a survey of 

 native material should be instituted in the interests of 

 plant breeding. 



The experience of European plant breeders tends 

 to show that old races of economic plants should not 

 be allowed to become e.Ktinct. Dr. Nilsson-Ehle. the 

 celebrated Swedish plant biologist, says, as quoted by 

 Mr. L. H. Newman in his book Plant Breeding in 

 Scandinaria, that 'even if the new sorts actually are 

 superior to the old sorts, and deserve to be spread, it 

 may be insisted that by displacing the old so-called 

 native sorts there may be a danger of losing for all 

 time many valuable constituents which they may 

 possess, and which might become of value in breeding 

 work.' Mr. Newman goes on to say that this would 

 seem to indicate the advisability of a breeding station 

 adopting some definite plan whereby representative 

 cultui'es of the best old races may be retained, in order 

 that a perennial source of new selection and material 

 for continued crossing work may thus be provided. 

 Mr. Harland suggests that much could be done by the 

 existing Botanic Stations in these islands, in making 

 and preserving collections of this kind. 



In connexion with the advocacy of the growing of 

 pure strains of cotton referred to in the editorial of our 

 last issue, it was pointed out by Mr. W. Nowell at the 

 West Indian Cotton Conference held in St. Kitts in 

 UJlt). that 'there were dangers in restricting seed selec- 

 tion to narrow limits. At the present time there were 

 good many different strains exhibiting great similarity, 

 but still possessing differentiating characteristics. If a 

 strain was selected which had certain of these particular 

 characters, and this were exclusively grown, some 

 characters possessed by other strains would be lost. 

 Provided the lint was satisfactory, mixed types were 

 .safer, because more capable of adjusting themselves to 

 their environment, including diseases which might at 

 any time occur. Moreover, should the circumstances of 

 the market so change that the type which bad been put 

 into cultivation was no longer the most desirable, and 

 it becauie necessary to recover the characters lost in the 



other strains, the planter would be limited and narrowed" 

 down to selection from that one type fi.r which the- 

 demand had declined 



Examination by Mr. S. C. Harland, the Assistant 

 for Cotton Research, attached to the Imperial Depart- 

 ment of Agriculture, conducted on a broader basis 

 than that from which the original selection was made, 

 of certain approximately pure strains already in culti- 

 vation, has shown that certain characters of value 

 have actually been bred out in securing others regarded 

 as of primary importance. 



It would seem, therefore, that Mr. Harland's sug- 

 gestion of collecting and preserving various strains of 

 cotton in special plots of the Botanic Stations in the 

 islands where that crop is cultivated, would be highly 

 advantageous, and would at the same time in no way 

 interfere with careful selection in planting the type at- 

 present found most desirable. 



USE OF PRICKLY PEAR SAP IN 

 ARSENICAL SPRAYS. 



A note in the lounial </' Agriculture Tropkale, April 

 1916, draws attention to the value of the sap of the prickly 

 pear in preparing arsenical sprays. It is of importance to 

 impart to these sprays the greatest possible adhesive power, 

 not only that they may exercise their effect as long as possi- 

 ble, but also that the least possible quantities of them may 

 be used to obtain the desired purpose. Kxperiraents, under- 

 taken by the Bureau of Eatoraology of the United States , 

 on prickly pear stems, have given good results in determin- 

 ing the manner in which these stems may be used. 



To begin with, the stems, cut into thin slices, are |mt 

 to soak in the receptacles for the preparation of the sprays. 

 To obtain the best result the stems should be cut in such 

 a manner as to ensure the rupture of all the cells which 

 contain the mucus which possesses the adhesive property. 



It is remarked that the eftect is not the same with all 

 insecticides. In fact, arsenate of zinc gives the best result, 

 then comes Paris green, but the results are almost negligible 

 with arsenate of lead, or with the salts of iron. About 

 10 kilos of cactus stems are used with about 75 litres of 

 water, and the required quantity of the ars^enical insecti- 

 cide added to the solution. This infusion of cactus leaves 

 in water keeps for a very long time before its mixt'ue with 

 the salt, if only a little sulphate of copper be added to it. 



The comparison of prickly pear with other adhesive 

 substances employed in the preparation of ar,-enical sprays is 

 in favour of the former from the point of view of its 

 efficaciousness: and this advantage is increased by the fact 

 that in most oases prickly pear is found in the neighbourhood 

 of new agricultural undertakings where it can be collected 

 at little expense. 



Prickly pear has become such a pe.^t in many countrie.< 

 where it has been iii'rodiiced, notably in South -Vfrica and 

 Queensland, that the possibility '.f its employment for some 

 useful purpose seems worth drawing attention to. and the 

 method of thu.s employing it. as described above, appear- t» 

 presetvt no difficulty. 



