136 



THE CANADIAN HORTICULTURIST. 



THE POTATO ROT,— ITS CAUSE AND 



REMEDIES. 



By J. Hoyes Panton, M.A., Professor of Natural His- 

 tory at the Ontario Agricultural College. 



The use of the microscope in the fields 

 of scientific research has revealed much 

 that is of importance to man. Many 

 forms of disease, about whose origin 

 little was known, have had much light 

 shed upon them since this instrument 

 was employed in their study, both 

 among animals and plants. We find 

 now that man is constantly lashed by 

 invisible foes — some attacking himself 

 and others the food which he eats. 

 During the past summer and fall a 

 striking example of this occurred in the . 

 prevalence of the so-called " potato rot," 

 which has proved a great loss through- 

 out the Province and in many parts of 

 the United States. In the bulletin 

 issued in November from the Bureau 

 of Industries, we learn that the " rot " 

 prevailed through the whole southern 

 belt of the Province. In many cases 

 one-half to three-fourths of the crop 

 was destroyed, and in some it was not 

 worth digging. With such disaster 

 around us, the questions are naturally 

 suggested. What is the cause of the 

 *' rot ? " and. What remedies can be 

 adopted *? 



Cause. — This disease has received a 

 great deal of attention from botanists 

 since the days when it became a scourge 

 in Ireland and other parts of the British 

 Isles, and it is now conceded to be the 

 result of a minute fungus called Phyto- 

 phthora infestans. This attacks all 

 parts of the plant — leaf, stem and 

 tubers. By those ignorant of the life 

 history of this tiny i)arasitic plant little 

 attention is paid to its appearance on 

 the tops, and no alarm is experienced 

 until the potatoes are affected. But 

 being very contagious, its presence on 

 the leaves should become a serious mat- 

 ter, especially when we remember that 

 it spreads with great rapidity. It is 



usually indicated by the tops presenting 

 a blotched, brownish, spotted, dead ap- 

 pearance. A close examination of the 

 potatoes showing this will discover in- 

 numerable slender stems growing up 

 out of the surface of the leaves and 

 stems of the affected plants. These 

 branch and swell out at the ends into 

 pear-shaped minute bodies (spores), 

 which are produced by millions. When 

 ripe they separate from the stem and 

 being exceedingly light pass into the 

 atmosphere, where they are wafted 

 about, many of them finally reaching 

 the ground or settling upon plants. 

 Under favourable conditions of mois- 

 ture and heat the contents of a micro- 

 scopic spore may push out a long minute 

 tube, which can penetrate into any part 

 of the potato plant and give rise to the 

 fungus ; or may separate into several 

 distinct portions (swarm spores) which 

 burst through the spore-wall and become 

 the source of the parasitic plant. The 

 mature plant which lives in the tops 

 and tubers is very minute, and can be 

 seen only by the aid of the microscope. 

 It consists of many colourless, branch- 

 ing, thread-like structures. These pene- 

 trate the tissues of the potato and feed 

 upon the juices, so that it soon weakens 

 and begins to waste away. From the 

 thread-like structures tiny stalks arise, 

 assuming beautiful plant like forms and 

 bearing upon their branches the spores 

 already referred to. They live but a 

 short time, but the thread-like structure 

 is perennial and hardy, and from frag- 

 ments of it new fungi may arise. It 

 is said by some that another kind of 

 spore is produced which can winter, and 

 thus give rise to the organism in another 

 season. These are the so-called resting 

 spores, apparently for the purpose of 

 keeping the species over certain periods, 

 while the spores already considered are 

 produced rapidly so as to hasten the 

 spread of the fungus under favourable 

 conditions. This minute microscopic 



