1136 



PBAGTICAL GUIDE TO GARDEN PLANTS 



POTAT& 



Diseases. — The most dangerous disease 

 of the Potato is that known as Phyto- 

 phthora imfestans. This is a parasitic 

 fungus which finds a congenial home 

 on the Potato-plant and utterly ruins it. 

 When a spore settles on a leaf, especially 

 if damp or wet, its root-like portion or 

 ' mycelium ' pierces the skin and bran- 

 ches about anaong the cells beneath, 

 absorbing their contents. In due course 

 it sends up on the siurfaoe, usually through 

 the small pores or stomata (see p. 33), 

 slender branching stems each ending in 

 a roundish bag-like structure which is full 

 of new spores. When fully ripe these 

 little boxes or ' conidia,' as they are called, 

 burst, and their contents are scattered in 

 all directions by the wind. These spores 

 undergo various changes but are capable 

 of retaining their vitality for several years 

 until they fall upon a congenial spot. It 

 was through their agency that the great 

 famine was produced in Ireland in 1845, 

 although their nature and life history were 

 not understood tiU many years afterwards 

 when they were discovered by the well- 

 known mycologist Mr. Worthington G. 

 Smith. The only evidences of this virulent 

 disease noticeable with the naked eye are 

 the brownish streaks and blotches on the 

 stems, leaves, and tubers. A microscope is 

 required to see the branches, spore cases 

 &c.' 



Once this disease takes a firm hold 

 upon a crop it is almost impossible to save 

 the plants, and the only thing that can be 

 done is to prevent the disease spreading. 

 Spraying the plants with Bordeaux mix- 

 ture (sulphate of copper) is a preventive 

 against spreading the disease, but seems 

 to be in no way capable of lessening it, 

 once it has taken hold. Indeed, according 

 to Mr. A. W. Sutton of Beading, who con- 

 ducted some experiments with spraying, 

 there is very little difference between a 

 plot of sprayed and unsprayed Potatoes. 

 Two plots which had been experimented 

 upon produced the following results. The 

 one which had been sprayed 3 times in 

 the season bore 3 cwt. 1 qr. 25 lbs. of 

 Potatoes ; the other, which had not been 

 sprayed at all, 3 cwt. 1 qr. 4 lbs. — that is 

 21 lbs. less than the other. ' Strange to 

 say,' continues Mr. Sutton, ' the quantity 

 of diseased tubers was precisely the same 

 in both plots, viz. 4 lbs. It is therefore a 

 question whether the additional weight 

 per acre would compensate the grower for 

 the somewhat laborious task of spraying 



his crop three times during the growing 

 period.' 



Among other remedies or rather pre- 

 ventives against the Potato disease are the 

 Rotation of Crops (p. 1104), not too thick 

 planting, light well-drained and well-tilled 

 soil, the application of artificial instead of 

 farmyard manures (p. 74), and the com- 

 plete burning of the decaying stems, 

 diseased tubers and leaves after the 

 Potatoes have been lifted. 



Other enemies of the Potato are wire- 

 worms, aphides, and various caterpillars, 

 but these may be kept in check by dust- 

 ing the rows and plants with lime and 

 soot at the time of planting, and after- 

 wards when the tops are wet with dew. 



VARIETIES OF POTATOES 



Potatoes are usually classed as 'kidney' 

 or ' round,' according to shape, but there 

 are now so many intermediate forms- 

 between those recognised as true ' kidneys ' 

 and true ' rounds ' that the distinction is 

 practically worthless. Indeed forms of 

 the two groups often get hopelessly mixed 

 at exhibitions and are passed over by con- 

 noisseurs with a shrug of the shoulders. 



The varieties also are extremely 

 numerous, and new names are added 

 each year, but it is very rarely one of 

 them proves of sufficient value to become 

 generally cultivated Kke some of the varie- 

 ties which experience ^as proved to be 

 worth a place in the garden. 



In selecting ' seed ' Potatoes, it may 

 be advisable to state that a change of 

 seed is a good plan. Many gardeners 

 save their own seed, and produce crops- 

 from their own stock for several years. 

 By-and-by, however, they do not bear so 

 well and become more or less subject to 

 disease, although the cultivation may be 

 perfect in every detail. It is then advis- 

 able to obtain new stock from a different 

 part of the country, and all the old vigour 

 will be re-established. 



The following varieties are among the 

 best grown : — 



Myatt's Prolific Ashleaf. — An excellent 

 kidney variety, very prolific, with good 

 quality and flavour. 



Veitch's Improved Ashleaf. — A heavy 

 cropper, fine flavour, and good for frames 

 or early crops. 



Beauty of Hebron. — ^An early and very 

 heavy cropper, with a tinge of pink round 

 the eyes. 



