INTRODUCTION. 



5 



I. -INTRODUCTION. 



The diseases to which our various cultivated fruits are subject have only attracted general 

 attention since they have been grown on a comparatively large scale, for when grown merely 

 for domestic use the relatively small number that were unfit for consumption did not count for much 

 from a monetary point of view, although the loss was keenly felt. But when cultivation was extended 

 and the products became of commercial importance, then the losses came to be reckoned in financial 

 terms, and it was felt that, in order to secure profits, it was necessary to avoid losses by disease or 

 otherwise as much as possible. 



Confining our attention to the Apple, which is the particular fruit to be considered here, as 

 orchards increased in size and apple-growing became a recognised industry, there was a 

 corresponding awakening on the part of the orchardist to the numerous foes with which he had 

 to contend. 



At first, in the absence of any definite knowledge, the nature and cause of disease were shrouded 

 in mystery, and the ancients often associated it with an offended deity, or regarded it as the working 

 of an evil spirit or humour which entered into the plant and deranged its functions. Then, in more 

 recent times, the weather was held responsible for the majority of diseases, and since the weather 

 could not be controlled, the hopeless apathy thus engendered found expression in the common 

 saying, " What can't be cured, must be endured." 



But some of the more intelligent and observant orchardists recognised that while the soil 

 and the climate, the heat, and the moisture may affect the fruit injuriously, there are other agencies 

 at work, such as various living organisms, which may induce disease and even cause the death of 

 the trees. 



The action of insects in destroying the fruit was too patent to escape observation, and the 

 worm-eaten apples due to the Codlin moth were familiar objects in the orchard, until a preventive 

 was found in spraying with arsenical compounds. 



The parasitic fungi which play such an important part in producing disease are usually very 

 small or microscopic forms, and their power for mischief was not recognised so readily or so early 

 as in the case of insects. But here, also, the union of exact observation with experiment and the 

 scientific study of the particular organisms causing the disease enabled remedial measures to be 

 adopted. The "Black-spot" or "Scab" of the apple, which was formerly regarded as "all 

 weather," is now known to be caused by a parasitic fungus, which can be kept completely in check 

 by spraying with Bordeaux mixture or lime-sulphur compounds. 



It wan natural that the minute and obscure micro-organisms, such as bacteria or microbes, 

 should be studied later, and the bacterial diseases of plants are now fully recognised and are being 

 successfully investigated. 



But with the more extensive and intensive cultivation of the apple, and the greater attention 

 that is being paid to everything which affects the quality of the fruit produced, certain obscure 

 diseases are cropping up and coming into prominence, which are due neither to insects nor to fungi, 

 nor even to the ubiquitous bacteria. 



Such is the " Bitter Pit " of the apple and pear, which was only so named as recently as 1895, 

 but, like many other diseases of plants and animals, existed long before that date, under various 

 other names. The success already achieved in connexion with the treatment of plant diseases 

 encourages us to hope that even such well-marked diseases of unknown origin as Bitter Pit, when 

 thoroughly investigated, may become amenable to treatment. The necessity of checking, if 



