ii4 BIOLOGICAL PROBLEMS 



e.g. to find wheats capable of tillering, of standing 

 up, or of " corning out", i.e. yielding a high pro- 

 portion of good plump grain, and then to breed these 

 qualities into varieties lacking them but possessing 

 other desired qualities. 



The other method is to try to discover the signifi- 

 cance of the property itself: the cause of the strength 

 of the straw, the meaning of corning out and of tiller- 

 ing, and then to go a step further, and try to control it. 

 The first method achieves results, but the second is 

 the more satisfying, and, in the end, the more certain. 



Finally, there is an important aspect which has not 

 yet received the attention it deserves. Crops must be 

 produced without the competition of weeds and free 

 from the depredations of fungi, insect pests, bacteria, 

 and other organisms that attack them.* The mortality 

 among plants is probably at least as great as the 

 mortality among animals or children, and yet we 

 make very little attempt to deal with it. Plant patho- 

 logy is almost a new subject. 



One of the most important crops for the plant 

 pathologist to investigate is clover. This crop might 

 be made the basis of our farming ; it grows extremely 

 well, produces one, and in the case of some varieties 

 two, good crops a year of most excellent animal food, 

 and when ploughed in adds to the soil great stores 

 of nitrogenous organic matter built up with the co- 

 operation of nitrogen-fixing organisms growing in 

 the nodules of its roots. Excellent crops of wheat can 

 be obtained after a good crop of clover. 



But unfortunately the crop is peculiarly liable to 

 disease. In some cases it cannot be grown oftener 

 than once in six or eight years, or occasionally 

 even longer. Two pests are known --an eel worm 

 (Tylenchus devastatrix) and a fungus (Sclerotinia). As 

 to possible treatment, however, nothing is known. 



