BIOLOGY IN ITS WIDER ASPECTS 1287 



recklessness; and so we turn towards reclaiming their respective 

 areas, and often towards afforestation anew, the former especially so. 



Over increasing areas, even on the Mediterranean, yet more in 

 India, and above all in Australia, we see the spread of the "prickly 

 pear" cactus (Opuntia), as a veritable curse, of which present 

 methods of extirpation are far from easy, or even adequately 

 successful. Yet the study of such unpleasing prickle-patches reveals 

 that they are actively serving nature's end, by renewing soil; and 

 next that as this soil forms, other species begin to appear among 

 them ; which indeed sometimes begin to replace them, by spreading 

 over them and robbing them of the full sunshine they require. With 

 further study, and due experiment, the ecologist may thus become 

 of substantial reclamation-service over areas deteriorated and 

 infested. 



Again, with the ever-increasing world-demand for paper, we are 

 becoming as it were sub-foresters, for its useful plants. And with 

 the advancing chemistry of cellulose, and its potential transmuta- 

 tions, as to glucose, etc., and with ferment ability also, we have 

 before us sources of food and of power, which point to a great future 

 for "weed-farming". Indeed, this at many points seems destined 

 to be at once more easy and more profitable than has been or can 

 be our traditional farming, with its costly wars with weeds ! 



Plant-breeding. — One of the most substantial examples of the 

 high economic value of careful plant-breeding is afforded by the 

 current advances in the quantity and quality of potato-crops, and 

 the increase of their immunity to diseases. The great famine of 

 Ireland three-quarters of a century ago was but the extreme case 

 of such calamity; and to have since produced, by selection and 

 from new sowings, varieties at least more and more immune to 

 Peronospora, was one of the great achievements of the breeder's art, 

 even before its Mendelian impulse. But there are only too many 

 other diseases; as from leaf-curl and mosaic to scab and other 

 pests upon the tubers. In such cases the mycologist and bacteriolo- 

 gist give valuable aid; and their colleague the entomologist has also 

 had his turn, as notably with the famous Colorado beetle, which his 

 vigilance is now checking from widening havoc. The breeder's 

 art, however, remains the central one. The climate of Scotland, as 

 especially that of West Lothian and Angus, has proved peculiarly 

 favourable for such skilled and selective cultivation ; the more since 

 seasons otherwise ungenial may give the best results. For the appa- 

 rent hardship of having to lift a crop of potatoes which cold and 

 lack of sunshine have kept small-sized and imperfectly matured, 

 often carries with it the compensation that such tubers, planted as 

 "seed", may give more vigorous plants and better yield than do 

 ordinary matured ones; so that the light crop, otherwise only fit 



