NATURE 



409 



THURSDAY, SEPTEMBER 19, 1S72 



THE POTATO DISEASE 

 II. 



TH E habits of the fungus which produces the potato 

 disease, Bolrytis or Pi-ronospora infcstaiis, have 

 been closely investigated by Montagne, De Bary, and 

 Berkeley. The latter gentleman has described its life- 

 history in the Gardener's Chronicle, and the editor of that 

 paper kindly permits us the use of the accompanying 

 woodcuts, which illustrate Mr. Berkeley's paper. The 

 fungus bears abundance of spores on the tips of the 

 branches, the mycelium, or spawn, burrowing amongst 

 the cellular tissue of the leaf and causing rapid decompo- 

 sition, while the vertical threads which branch and bear 

 the spores, find their way through the stomata, or leaf 

 pores. Tlie spores themselves, falling on different parts 

 of the plant, germinate, and, penetrating the tissues, pro- 



/. Pfronospora infestcins. 



1. The .vime, burrowing amon^ the tissues of the leaves, nnd maknig its 

 V ay through the stomata. 



duce a brown tint, not only in the cells with which they 

 are in immediate contact, but also in the adjacent cells. 

 In addition to these spores, or, more correctly speaking, 

 conidia, the fungus produces also zoospores, or moving 

 spores, furiiished with the well-known movable threads or 

 processes, and which are differentiated from the contents 

 of some of the ordinary spores. These bodies, hl^e the 

 ordinary spores, germinate and penetrate the tissues, 

 producing the same brown tint, and in the same way as 

 the kind already mentioned. 



The fungus was unknown to the older mycologists, 

 having, at all events, never attracted attention before the 



VOL. VI. 



first great outbreak of the potato-blight in 1S45. It is not 

 quite peculiar to the potato, being found also occasionally 

 on other plants belonging to the natural order Solanacea?, 

 especially on the fruit of the tomato. The first indication 

 is the well-knoun brown spots on the leaves of the plants ; 

 but by the time it manifests itself in this manner, its 

 mycelium has already made deep inroads into the cellular 

 tissue of the leaf and stem, and cure is well-nigh hopeless. 

 The cutting-off of the haulm close to the ground will 

 generally prevent the spread of the disease to the tubers, 

 but this remedy is at the risk of destroying the quality of 



3. Spores, or, more properly speaking, conidia, germinating. 



4. The same, sown artificially, and penetrating the tissues a^ter eighteen 



5. Spores with contents differentiated. 



6. Zoospores. 



7 Zoospores germinating. 



the crop, since it is impossible for the tubers thoroughly 

 to mature after the entire removal of the vegetative 

 organs. The growth of the fungus is greatly promoted by 

 wet weather, and the " sowing " over the crop of lime, 

 which acts as a powerful desiccant, is therefore a natural 

 remedy, as also is the application of soot, the properties of 



8. Zoospores ! 

 penetrating the 



artificially in the stem, and after twenty-four 

 3 and entering the intercellular spaces. 



carbon as a disinfectant and absorbent of gases being so 

 well known. Prof. Gardner states that the diseased 

 tuber is strongly alkaline, from the presence of ammonia, 

 the sound potato having an acid reaction. Since, also, we 

 are commonly visited by heavy showers during the latter 

 part of July and early part of August, the period when 

 the disease generally first decidedly manifests itself, it i; 

 probable that the advice of the Gardener's Chronicle is 

 sound, to plant chiefly early varieties, and lift early, 

 though this will involve some loss to the productiveness 

 of the crop. On all these points, however, we are greatly 

 in want of the authoritative opinion of practical men, the 

 result of a careful series of experiments from which all 

 accidental causes have been eliminated. The Royal 

 Horticultural Society has a fine opportunity of performing 



