43i HemarJcs and Observations suggested 



cause ; but from the experiments of Mr. Knight, quoted here by 

 Dr. Lindley, it appears that, like as with thorns, the want of 

 water is often the principal cause, perhaps by occasioning a stag- 

 nation in growth, and thus furnishing a nidus for the seeds of the 

 fungus. Some disapprove of manure to peas, but others that 

 dung heavily have good crops ; in very wet cold seasons, as the 

 present, manures may retain too much water, but generally 

 should be useful in preventing stagnation, which seems to be the 

 cause of the fungus settling on the leaves. I have been often 

 puzzled with the appearance of mildew among seedling larch. It 

 is frequently the case where seedling larch are grown to any 

 extent, especially after being grown some years on the same spot, 

 though in rotation only, to have the seedlings go off in July 

 and August, in round patches that increase in size, but generally 

 preserve the circular form like the fairy rings of fungus. I have 

 heard this ascribed to improper manure, but have seen it take 

 place with all sorts of manures. I never could perceive, after 

 minutely searching the ground, any insects in quantities that 

 were likely to cause the mischief observed ; but have found the 

 outside of the circle, at the surface of the ground, covered with 

 a web of minute hairs similar to the mildew in frames ; and as 

 the plants die first at the surface when the tops and roots are 

 quite fresh, I think the mildew or fungus must be the cause of 

 their death, but have been puzzled v^^hat is the cause of the 

 fungus. It is quite different from that on the thorns and peas, and 

 similar to the one in frames, which is generally allowed to be 

 caused by damp and want of air ; this cannot be the case with 

 the seedling larch, as we have observed it in airy places, and all 

 kinds of weather and soil : perhaps it is not the same, though 

 similar; and the seed of the fungus, deposited and accumulated in 

 old soils, may spread in rings as other fungus do, and might be 

 best stopped by spreading lime or salt, if necessary, round the 

 ring to prevent its increase. * The rules given by the professor, 

 at the end of the section on Atmosphei'ical Moisture, should be 

 carefully committed to memory. 



The next subject, of Ventilation, has been largely and ably 

 handled of late in the Magazine. Dr. Lindley shows the neces- 

 sity of ventilation to respiration, in carrying off noxious vapours, 

 and producing dryness and cold ; he also quotes Mr. Knight for 

 its necessity in giving motion to plants, and increasing the circu- 



* We have had a fungus amongst our willaws for some years, of a bright 

 orange colour, which is a clear proof of the belief that the smut in wheat 

 may be got from the soil as well as the seed. The first year of its appearance, 

 we observed it on the leaf only ; now it is frequently to be found in the mid- 

 rib of the leaf, and on the stem ; and on examining with the microscope, the 

 fungus may be traced a good way below the bark, which is heaved up from 

 the inside outwards, — a clear proof that the fungus exists in the sap of the 

 plant, and must have been absorbed by the root. 



