130 



HISTORY OF THE VEGETABLE KINGDOM. 



in the manure or the soil, and enter by the pores 

 of the root. Tliis fungus is known among far- 

 mers by the name of the red rust, and as it af- 

 fects the stalk and leaves only, it does not ma- 

 terially injure the crop. There is another species 

 of fungus known to the ftirmer by the name of 

 red gum, which attacks the ear only, and is ex- 

 tremely prejudicial. In the aggregate it consists 

 of groups of minute globules, interspersed with 

 transparent fibres; the globules are filled with a 

 fine powder, which explodes when they are put 

 into water. It is very generally accompanied 

 with a maggot of a yellow colour, which pro- 

 duces a flv, well known as the destructive wheat- 



Smia is a disease extremely frequent in cul- 

 tivated corn. It consists of a conversion of the 

 farina of the grain, together with the integu- 

 ments, and even part of the husk or pericarp, 

 into a black soot-like powder. If the injured 

 ear is struck with the finger, the powder wiU 

 be dispersed like a cloud of black smoke; and if 

 a portion of the powder is wetted hy a drop of 

 water, and put under the microscope, it will be 

 found to consist of millions of minute and trans- 

 parent globules, which seem to be composed of 

 a clear and glairy fluid, encompassed by a thin 

 membrane. This disease does not affect the 

 whole body of the crop ; but the smutted ears 

 are sometimes very numerously dispersed through 

 it. Some have attributed it to the soil in which 

 the grain is sown, to the manure, or to contam- 

 ination of the seed. This latter is the most 

 likely cause, a.s Willdenow regards it as origin- 

 ating in a small fungus plant, which multiplies 

 and extends till it occupies the whole car. As 

 a proof that the minute seeds of this fungus 

 may attach themselves to the grain, it is found 

 that washing the seed with a solution of arsenic, 

 or sulphate of copper, of such strength as to 

 destroy the vegetating power of the parasitic 

 plant, but not the germ of the grain itself, will 

 effectually prevent the recurrence of smut. A 

 modification of this disease usually seizes on 

 ears of wheat, and is called by the fanner smut- 

 ball. In this case, the cotyledons only are con- 

 verted into a black mass, while the enveloping 

 membranes remain sound. The ear is not much 

 altered in its external appearance, and the dis- 

 eased grain contained in it will even bear the 

 operation of thrashing; and thus the fungi mingle 

 with the bulk, and of course tend to propagate 

 the same disease, if the grain be used for seed. 



Mildew consists in a thin whitish coating with 

 which the leaves of vegetables are sometimes 

 covered, causing their decay and death, and of 

 conseriuence an interruption of the functions of 

 the plant. It is frequently found on the leaves 

 of tmsilago farfara, humulus lupulus, coryhis 

 avellana, and the white and yellow dead nettle. 

 It is also found to attack wheat fields, in the 



form of a glutinous exudation. According to 

 Willdenow, it is occasioned either by the growth 

 of an exceedingly minute fungus, the mucor 

 eresi/phe of Linnscus, or by a sort of whitish 

 slime, which a species of aphis, or plant louse, 

 deposits upon the leaves. Soot is said to pre- 

 vent its occurrence. 



Honey dew is a sweet and clammy substance 

 which coagulates on the surface of the leaves 

 during hot weather, particularly on the leaves 

 of the oak tree and beech; and is regarded by 

 some as the excrement of the plant louse, while 

 others look on it as an exudation of the juices 

 of the plant. The leaves of the beech tree on 

 the occurrence of an unfavourable wind, become 

 covered with a glutinous coating, similar in 

 flavour to the fluid obtained from the trunk, and 

 in every respect resembling the honey dew of 

 other plants. Saccharine exudations are fre- 

 quently found on the leaves of many plants, 

 though not always distinguished by the name 

 of honey dew, which term should be applied 

 only when the exudation is in such excess as to 

 cause disease. For if it is to be applied to all 

 saccharine exudations whatever, these must be 

 included under the term honey dew: the sac- 

 charine exudation observed on the orange tree, 

 by De la Hire, together with that on the lime 

 tree, which is more glutinous; and of the poplar, 

 which is more resinous, as also that of the cistus 

 creticus, from which the gum resin labdanum is 

 collected by means of beating the shrub with 

 leathern thongs, and of the manna which exudes 

 from the ash tree of Italy, and the larch of 

 France. It is also possible that the exudation 

 of excrement constituting honey dew, may oc- 

 casionally occur without producing disease; for 

 if it should happen to be washed off soon after 

 by rains or heavy dews, then the leaves wiU not 

 suffer. 



Dropsy. When the atmosphere is surcharged 

 with moisture, or too much water is applied to 

 the roots of plants, an excess of their juices oc- 

 curs, which has some resemblance to the dropsy 

 of animals. That is, their absorbing actions 

 become too great for their exhaling. Willdenow 

 describes it as occasioning a preternatural swell- 

 ing of particular parts, and inducing putrefac- 

 tion. It occurs chiefly in bulbous and tuberous 

 rooted plants, which are often found much 

 swelled after rain. It affects fruits also, which 

 it renders watery and insipid. It prevents the 

 ripening of seeds, and occasions an immoderate 

 production of roots from the stem. Succulent 

 plants in particular are apt to suffer from too 

 profuse waterings ; and the disease thus occa- 

 sioned is generally incurable. The leaves drop 

 even though plump and green; and thefiniit rots 

 before reaching maturity. In this case, the ab- 

 sorption seems to be too great, in proportion to 

 the transpiration; while a soil too richly manured. 



