KEPOET OF THE BOTANIST. 83 



planter or horticulturist, or about svliicli more has been said and writ- 

 teii, than those produced by members of the small order, Feronosporecc. 

 About forty species are known to occur in the United States, and, al- 

 tlioupli few in numbers, a glance at the injury they occasion will show 

 the importance of a complete knowledge of their habits and method of 

 development. All the species, with the exception of those of the genus 

 Fythiiim, one of which is supposed to be the pottiug-bed fungus, so de- 

 structive to joung house plants in the winter, attack living plants. 



I'otato rot, or murrain, is caused by Phytophthora in/eatans, better 

 known as Feroiiospora iiifestans. Wherever potatoes are grown, this 

 potato fungus is liable to occur. Last year it destroyed one-third of the 

 potato crop of New York State, and it is not uncommon to hear from 

 certain sections of the entire destruction of the crop by this disease. 

 Other members of tlie family o-f plants to which the potato belongs aiso 

 suffer from the attacks of this fungus. It is a serious enemy to the to- 

 mato, both in this country and in England. W. G. Smith states that in 

 t-ome districts in England, the out-of-door culture of the tomato has been 

 quite stopj>id by the ravages made upon it by the potato fungus.* 



The vegetative system of the potato fungus grows within the tissues 

 of the leaves, stems, and even penetrates to the underground portions 

 of the plant, attacking the tubers themselves. This vegetative system 

 dies with tbe death of the i)arts in wluch it grows. The part above 

 ground is killed in the fall, but the mycelium that has entered the tubers 

 may retain its vitality and begin a new growth in the sprouts of the fol- 

 lowing year. Whether the disease is continued in this vray is not posi- 

 tively" known. It is well known, however, that a peculiar form of spore, 

 popularly referred to as the resting or winter spore, is formed within the 

 tissues infested by the fungus. These resting spores may be found in 

 tlie 'decayed tops of the potato, but they are especially abundant in the 

 diseased'^tubers. Their oflice is to preserve the existence of the fungus 

 through the winter. In the spring they germinate and produce a new 

 crop of the fungus. The importance of totally destroying all parts of 

 the plants that have suflered from the attacks of the fungus is self evi- 

 dent. There is another form of spore of the potato fungus that is pro- 

 duced in the eummer upon the under surface of the leaves of the infested 

 plant. When the conditions are favorable for the production of these 

 summer spores — conidia — the mycelium within the tissues sends out 

 branches into the air through the breathing pores — stomata of the leaf — 

 and it is upon these branches that the conidia are formed. The issuing 

 of these branches from the leaf impart to the lower surface a frosted ap- 

 pearance. The conidia are produced in the greatest abundance, and 

 successive crops rapidly follow each other. These couidia, falling upon 

 the leaves, quickly germinate, under the proper conditions of humidity, 

 and the disease is thus spread from plant to plant and field to field, 

 sometimes appearing over large areas with a suddenness that might 

 well bo attributed to magic or witchcraft by the tmeducatcd. 



There is no known remedy against the ])Otato disease. ^S'o special sys- 

 tem of culture can be relied on to i)revent it. Mr. W. G. Smith, in his 

 little book on the "Diseases of Field and Garden Crops," treats at some 

 length upon the potato disease. He says : 



To prevent the annual recurrence of the potato murrain, it ia iu the highest degree 

 necessary to destroy tbe material (dead tops, &c.) which is r.ndoubtedly s^varming with 

 myriads of disease 'germs. Tliis destruction should he etTected by burning, or, where 

 burning is not practicable, deep burial might be resorted to ; no more fatal mistake can 



'Diseases of Field and Garden Crops, p. 275. 



