38 



NEW ENGLAND FARMER. 



For the New England Farmer. 

 POTATO-ROT, 



VEGETABLE 



IN CONNECTION WITH THE LAWS OF 

 GROWTH AND DECAY. 



BY PROF. J. G. HOYT. 



It is not wonderful, that the potato, constituting 

 as it does an important, and, in many cases, the 

 principal article of food throughout the civilized 

 world, should be a leading topic of discussion in 

 all our Agricultural journals. What ails it, and 

 what will cure it, are questions of absorbing inter- 

 est to every one who can wield a knife and fork. 



Amid the heterogeneous mass of testimony pre- 

 sented on the subject of the potato-rot, it is ex- 

 tremely difficult, if not altogether impossible, to 

 ascertain the truth. The witnesses on the stand, 

 embracing the most experienced agriculturists as 

 well as men eminent in science, contradict each 

 other on some of the most important points in the 

 case. Experiments, conducted apparently with 



equal care and skill, have led to totally different; propnated Jo the growth^ of jhe plant. jl his ear 

 results. There was "method" in Hamlet's mad- 

 ness, but there seems to be no method in the pota- 

 to-rot. Every sort of seed, prepared in every im- 

 aginable way, has been planted at every period in 

 the season, in every variety of climate and tem- 

 perature, on every kind of soil, dressed with every 



tant to know the part which these tops perform in 

 the economy of vegetation. The leaves of the 

 plant sustain towards the tuber the same relation 

 which the lungs of a man sustain to the human 

 body. They discharge two important functions : 

 the one of respiration, the other of perspiration. 



In the first place, then, the leaves are the respi- 

 ratory organs of the plant. The sap or blood of 

 the potato plant is not fit for the growth of the tu- 

 ber until it has undergone a certain chemical 

 change in the leaf, where it comes in contact with 

 the air. The fact that the peculiar mechanism of 

 the leaf does work a decided change in the sap of 

 a plant, is strikingly illustiated in the process of 

 grafting. The scion, and not the root or trunk of 

 the tree in which it is inserted, determines the 

 character of the fruit. Animals in respiration give 

 off carbonic acid and absorb oxygen ; plants, re- 

 versing this process during the day, absorb car- 

 bonic acid, which in the laboratory of the leaf is 

 analyzed, the oxygen thrown off and the carbon ap- 



bon not only furnishes the material for the woody 

 stalks and limbs, but, in the case of the potato, 

 contributes about one-fourth of the starch or nutri- 

 tive substance of the tuber. The moment, there- 

 fore, the leaves of the potato are from any cause 

 destroyed or rendered incapable of performing their 



species of manure, applied in every practicable de- duties, the sap ceases to be carbonated, and be- 



.! comes, as a necessary consequence, unhealthy and 



gree and manner, and yet the rot, without any ap 

 parent discrimination or regard to any regular sys- 

 tem of procedure, has committed its ravages alike 

 under all circumstances and in all places. Various 

 and contradictory theories in relation to the matter 

 have been advanced and defended, each in its turn, 

 with commendable zeal and activity. But if na- 

 ture, as Pope says with more truth than poetry, 



"Acts not by partial but by general laws," 

 laws simple and immutable, then every theory, 

 whether based on bolrytis or "black bugs," must, 

 to deserve our notice, accord in all its parts with 

 the laws of nature. The theory which seems to 

 us to harmonize best with the established laws of 

 vegetable growth and decay, and at the same time 

 to reconcile, to the greatest extent, the discordant 

 facts in the case, we will take the liberty to state 

 and explain, as briefly as we can. 



THEORY. 



The rot is not the result of accidental causes, 

 but is a disease, partly epidemic and partly hered- 

 itary. This disease may properly enough be 

 termed a dropsy, caused by an excessive accumula- 

 tion of unelaborated juices in the tuber. The 

 plausibleness, if not the truth, of this theory will 

 appear evident from several considerations. The 

 commencement of the rot in the tuber is, with very 

 rare exceptions, susceptible of philosophic explana- 

 tion, subsequent to the blight in the leaves. This 

 fact indicates, with sufficient plainness, that, the 

 disease has its origin in the tops. It is reasona- 

 ble, aside from the fact, that this should be the 

 case ; for the young potatoes have no function to 

 perform in the growth or decay of the plant — they 

 are merely incidental, and their entire destruction 

 should in the nature of things no more affect the 

 plant, than the decay of apples on a tree should af- 

 fect the tree. The fruit in each case is the passive 

 product, and not the active producer, of an organ- 

 ism over which it has no control. If, then, the 



stagnant in the stalk, until at length by mere force 

 of gravity it settles down through the cellular tis- 

 sue into the tuber. 



In the second place, the leaves are the perspira- 

 tory organs of the plant. The watery parts of the 

 sap are thrown oft" by the leaves, just as the watery 

 parts of the blood are thrown off by the lungs. 

 This is seen in the excessive perspiration which 

 constitutes mildew, as plainly as pulmonary vapor 

 is seen in a frosty morning. Now if the leaf is 

 unseasonably destroyed or blighted, the insensible 

 perspiration is checked, and all the vessels of the 

 plant become distended with a superabundance of 

 \ aqueous moisture. If the tops should be light and 

 the weather at the time dry and hot, evaporation 

 from the stalk might carry off the excessive sap 

 before it should become diseased and find its way 

 down to the tuber; but if the tops should be rank 

 and the weather wet, the sap would stagnate in 

 the stalks and result eventually in the rot. 



The whole process of the potato-rot, then, seems 

 to be this : First, the leaves are from some cause" 

 blighted. Secondly, the sap, excessive from want 

 of transpiration through the leaf and uncarbonated 

 from want of contact with the air, becomes dis- 

 eased, and finally settles down by its own weight 

 into the tube*. Under this pressure of circum- 

 stances, the tuber, surcharged and bloated with the 

 corrupt and fetid juices of the decaying plant, rots 

 as in duty bound. 



It may be proper in this connection to notice the 

 objection to this theory, growing out of the fact, 

 that the tubers do sometimes decay, as in the case 

 of Mr. Comings, before the leaves are blighted. 

 In all such instances, we have no doubt that the 

 seed, gathered probably from a rotten field, was to 

 a greater or less extent affected with the disease. 

 This disease, by the laws of "ordinary generation," 

 is transmitted from the "representative head" to 

 the descendants. Tops, roots and tubers are "al- 



potato-rot originates in the tops, it becomes impor- 1 together born in sin." The taint, which was 



