MILDEW. 



MILDEW. 



particularly that of wheat, are the following, 

 and in the order stated : Peat or moor, calca- 

 reous, calcareous loams, sand, sandy loams, 

 and another kind not found in any great 

 breadth, but* in patches, chiefly but not exclu- 

 sively in clayey soils. The practical farmer 

 calls it gray earth." (Egremont's Obs. on the Mil- 

 detv, p. 93.) 



The slightly superior power of clayey soils 

 to protect the crop growing upon them from 

 being the most severely affected by the mil- 

 dew, probably arises from the temperature cf 

 such soils being less liable than lighter ones 

 to sudden vicissitudes of temperature. Dr. 

 Hales found, in the month of August, when the 

 temperature of the air and of the surface of 

 the soil were 88, that the temperature of the 

 soil 16 inches below the surface was 70. In 

 October, when the air and surface were at 35, 

 the temperature at 16 inches beneath was 48, 

 and at 24 inches 50. This statement led me 

 to make a few experiments upon the compara- 

 tive rapidity of cooling, or, in other words, the 

 power of conducting heat of various soils; and 

 I invariably found, that the mercury in a ther- 

 mometer, whose bulb was buried equally deep 

 in a silicious, as those of others were in a cal- 

 careous and in an aluminous soil, rose most 

 rapidly, and that in the last-named most slowly. 

 Their rapidity of cooling followed the same 

 order. Some experiments substantiating the 

 same fact will be found in Sir H. Davy's Ag- 

 ricultural Chemistry, p. 179. Every gardener 

 knows the injury hi-s plants sustain from sud- 

 den vicissitudes of temperature. "Whatever 

 has a tendency to check a quick and great loss 

 of heat in the substances which surround such 

 vegetables, particularly their roots, will be best 

 calculated to save them from that injury, and 

 from vegetable death; consequently, those 

 earths which are the worst conductors of heat, 

 or, in other words, are the longest in heating 

 or cooling, will be most favourable in resisting 

 any sudden alteration, and the vegetables 

 growing on them will be the least injured 

 when so assailed." (Egremonl's Observations on 

 the Mildew, p. 30.) 



Situation appears to have rather more tute- 

 lary power than the soil, since I have invaria- 

 bly found the wheat growing in fields lying in 

 closely enclosed valleys more frequently and 

 more seriously injured by mildew than those 

 upon elevated exposures. ''A Lincolnshire 

 Farmer," Mr. Lambreth and other writers in 

 the forty-fourth vol. of the Annals of Agriculture, 

 agree in this observation, and it is no more than 

 might be anticipated from our knowledge of the 

 habits of the fungus tribe ; such situations being 

 always more damp, and subject to a moist, 

 foggy atmosphere. 



All varieties of wheat are liable to the disease, 

 but the white is always the earliest affected, and 

 the bearded or rivet the last. This may arise 

 from the latter variety having a firmer epider 

 mis, arising from its containing a little more 

 silex, and thence having its pores less easily 

 acted upon by atmospheric changes, and con- 

 sequently less liable to the entrance of the 

 seeds of this fungus. Moreover, the hardness 

 of the epidermis checks their rapid outspread 

 812 



when vegetating. Mr. Sirs considered spring- 

 sown wheat not liable to this disease of the 

 mildew, and that is the general opinion in 

 South Holland. Other authorities deny that 

 spring-wheat is exempted from it ; and to this 

 opinion I incline, in the absence of any thing 

 like decisive knowledge on the point. 



Early sowing is advisable, because the wheat 

 plants, by this means, have a chance of pass- 

 ing the time of blooming before they are ex- 

 tensively attacked ; and the more advanced the 

 growth of the seed, the more it is out of the 

 power of this parasite to check its perfection. 

 Another reason suggested by Mr. W. Jones, of 

 Wilmington, Somerset, is, that when sown late 

 the plants are green and sappy in July, and 

 even at the commencement of August, the sea- 

 son in which the cold and frosts occur that are 

 so inducive of the disease; and this green 

 state necessarily renders them more than ordi- 

 narily liable to suffer by such a reduction of tem- 

 perature. On this account it is that in super- 

 luxuriant crops,and plants growing upon dung- 

 hills, the former are liable to, the later almost 

 always are infected by, mildew. Yet the time 

 for sowing is no unfailing preventive, for in 

 "mildew years" all crops are attacked; and 

 instances have occurred where, in fields sown 

 in September, October, and November, the first 

 and the last have been most injured. 



The berberry has been anathematized as a 

 source of this vegetable pest; but I have never 

 yet met with any facts which establish the 

 charge. It is true that Rolesbury, in Norfolk, 

 is locally known as " mildew Rolesbury," and 

 that the berberry abounds in the neighbour- 

 hood of that village ; but I know many low- 

 lying arable districts, proverbially liable to the 

 mildew, having no berberries in their vicinity. 

 It is true that a band of mildew has been traced 

 across a field of wheat from a berberry bush 

 growing in one of its hedge-rows ; but then I 

 have seen a similar track of the disease com- 

 mencing from an oak. It is also true that Mr. 

 Knight, the late excellent president of the Lon- 

 don Horticultural society, found wheat, sprin- 

 kled with water, in which berberry branches 

 had been washed, speedily became infected 

 with the mildew ; but he also ascertained that 

 wheat sprinkled with clear water, became 

 similarly diseased. I have tried many experi- 

 ments, with a view to ascertain the truth or 

 error of this supposition, but have not suc- 

 ceeded. However, I am convinced that the 

 parasite which affects the berberry is not the 

 Puccinia graminis : the sporidia are dissimilar, 

 and the colour totally unlike; but it may be, 

 and certainly much resembles, the Uredo rubigo. 

 It is no objection to say that the identity is un- 

 likely, because the plants attacked are so 

 widely distant ; for, as already noticed, these 

 parasites will vegetate on very various and 

 even dead vegetable matters. The parasite 

 which infects the leaves of the berberry is the 

 JEcidium berberidis: it is a beautiful minute gas- 

 tro mycus, and there is no resemblance be- 

 tween it and the rust of wheat, except in colour. 

 It is a vulgar error to suppose that an JEcidium 

 on the berberry could produce a Puccinia on 

 wheat." See BERBERRY. 



