214 



Mildew. 



Vol. XL 



them in a clean cupboard, in which there is 

 no mouldiness, in the summer season — and 

 put the other at the same time in a similar 

 place, but near or in connection with a piece 

 of mouldy bread ; it will be found that the 

 mouldiness will be sooner and more abun- 

 dantly communicated to the latter. That 

 both will become mouldy at length is true, 

 because in the season that this fungus will 

 grow, its sporules will be conveyed by the 

 atmosphere in small quantity, but the 

 mouldiness will be completed much sooner 

 when the sporules are furnished at first in 

 quantity. 



In plants that flower once, bear seed, and 

 die, including annual and biennial plants, of 

 which wheat is one, the,^ital energy begins 

 to decrease shortly aftef the formation of the 

 seeds and before its ripening ; the absorb- 

 ents of the root cease to draw any support 

 from the earth; the lower part of the culm 

 or straw, becomes ripe, rigid and sapless, 

 whilst the upper part remains of a green 

 colour, and full of juices, which pass gradu- 

 ally from below upward, into the ears or 

 seeds; the straw gradually ripening upward, 

 as the sap in the straw goes, (probably by 

 capillary attraction) to perfect the grain. 



The mildew is frequently found upon 

 wheat before, or at the time of flowering, 

 when the stalk and sheath being in a vig- 

 orous growing state, do not suffer from it, 

 and it obtains no hold upon them ; but the 

 leaves having fulfilled their purpose, are 

 weak and become mildewed; the only dam- 

 age is, that the sporules are remaining on 

 the dead leaves in such quantity as greatly 

 to peril the crop, if circumstances favour- 

 able to their growth should take place, 

 when the straw becemes weakened before 

 ripening, and I very much doubt whether in 

 any case, a field becomes entirely discol- 

 oured with mildew in half a day as some- 

 times happens, except the leaves and 

 sheaths, had been mildewed previously. 



The particular fungus called mildew in 

 England, has been figured and illustrated by 

 Joseph Banks, President of the Royal So- 

 ciety, by coloured plates much magnified, 

 showing its growth, form, action and devel- 

 opement, and exhibiting the insertion of its 

 root-like appendages among the vessels of 

 the culm — this work, an octavo of a few 

 pages, I have not seen for years; and it is 

 probably scarce. It is in the Philadelphia 

 Library, No. 3759. 



I do not remember the name given by 

 Banks to the species described, but I believe 

 we have two species known as rust or mil- 

 dew. I have not examined them for some 

 years, having given up microscopical e.v- 



aminations, except in cases of great neces- 

 sity. I find in Eaton's manual of Botany, 

 two species marked as rust; viz. Puccinia 

 graminis and Uredo linearis. 



For the production of mildew on wheat, 

 it is necessary — 1. That the growth of the 

 wheat through age, poverty, or disease, be 

 weak and not vigorous. — 2. That the spo- 

 rule or seed of the mildew be present. — 3. 

 That from rain, or heavy dew, so much 

 moisture be present as will enable the spo- 

 rule to adhere to the culm. — 4. That the 

 heat be sufficient for its growth. When all 

 these circumstances are present, the growth 

 of the mildew on the straw is rapid, as the 

 colour of the straw is changed in a short 

 time — but several hours elapse before the 

 root-like processes of the mildew, inserted 

 between the plates and tubes of the culm, 

 are so large as to compress the vessels of 

 the culm and prevent the ascent of the sap. 

 As an evidence of this, it will be found 

 possible to clean the straw by rubbing or 

 vvashmg. But after a short time the root- 

 like processes, force themselves through the 

 plates and tubes of the straw, preventing 

 any movement of the sap. The stalk re- 

 tains its green colour, and does not ripen — 

 the grain receives no further addition from 

 the sap — the soft part evaporates and shriv- 

 els — and the injury seems to be nearly irre- 

 parable. The only mode of relief that I 

 have heard proposed, is to cut the grain im- 

 mediately when dry, bind it up, put it in 

 close shocks, and let it stand till dry. I 

 have tried this twice, and can only draw 

 upon my memory for the result, once with 

 partial success, and once without any: the 

 weather succeeding being not entirely dry. 

 I still believe, that if the straw and grain 

 were clear of any wet except the sap, and 

 the process of cutting and shocking care- 

 fully done, and the weather should remain 

 dry for a week, that the wheat would ripen, 

 and it is well established, that no advantage 

 is obtained by letting it stand uncut after 

 being mildewed. We can easily conceive, 

 that if the mildew is a fungus of the na- 

 ture of a mushroom, the close compression 

 in the sheaf and the exclusion of light and 

 air, may destroy it ; and when that is done, 

 the compression on the culm may cease, 

 and the attraction of the sap to the head be 

 resumed. It is now known that Indian corn 

 cut before it is entirely ripe, and put in 

 shocks, continues to ripen for a considerable 

 time. 



The poisonous nature of many species of 

 fungi — their action on the salivary glands, 

 and the suddenness of their appearance, lead 

 me to suspect that the slavering of horses 



