78 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



spore as that the oak tree had its origin in tlie acorn. These spores aro 

 all microscopic in size, some being so small that very high x^owers are 

 required to see them at. all, and they are usually formed in such im- 

 mense quantities that the number produced by a single individual i.s 

 absolutely inconceivable. The spores are very light, and when dry, 

 may be distributed by the slightest breath of wind. The wonder is 

 that auy plant escapes them. Were it not that occasionally certain 

 factors operate to prevent their distribution, and that their germination 

 usually depends upon a peculiar combination of circumstances, these 

 fungi would quickly effect the complete destruction of our crops. 



If a fungous disease appears suddenly in any given district or section 

 of the country, it is simply an indication that the temperature or other 

 atmospheric conditions have been favorable to the growth or develop- 

 ment of the fungus, the germs of which were already present. If we 

 can, by any means, prevent the spores of fungi from gaining access to 

 the plants upon which they are parasitic, there would be no surer way 

 of checking their ravages. To do this, however, except in a small way, 

 seems impracticable. In practice the efficiency of this plan is well 

 demonstrated by the pieans often employed to prevent the black rot of 

 grapes, i. e., by inclosing the growing clusters in paper bags. 



With few exceptions, dryness is incompatible with the developmoDt 

 of fungi, moisture is a sine qua non to their growth. In very dry 

 countries they are rare, and during seasons of protracted drought little 

 is to be feared from their attacks. Ileavy dews, rains, fogs, and a warm 

 , atmosphere saturated with moisture, on the other hand, most favor their 

 development. If we can keep our plants free from all moisture^ par- 

 ticularly from the condensation of dew upon their surfaces, we will se- 

 cure immunity from the attacks of some of our worst fungous enemies. 

 That this is true of the grape mildew {Peronosjyora viUcola) is attested 

 by the experiments of Mr. Saunders, who effectually prevented the 

 growth of this fungus by placing over the vines a temporary board 

 shelter extending a foot or so each side of the trellis.* 



Colonel Pearson states that by this simple contrivance, substituting 

 for boards a muslin covering, he has also protected his grapes from the 

 black rot.t 



As the growth of weeds may be checked by not allowing them to go 

 to seed, so may the ravages of fungi be diminished by preventing the 

 ripening of their spores. In some cases it may be practically impossi- 

 ble to accomplish this, but there are many species whose further pro- 

 pagation might be prevented with comparative ease by destroying them 

 before the spores are matured. In fact, this is apparently our only 

 hope in contending with certain species, as, for instance, the black knot 

 and the smut of Indian corn. In his paper on the black knot,:j: Dr. 

 Farlow, in speaking of the prevention of the disease, says : 



Frojn tlie kiiowledge that the knot ia a contagious disease, caused by a fungus 

 whose ascospores are ripened in midwinter, and whose mycelium does not extend for 

 more than a few inches below the knots, and bearing in mind that the fungus is in- 

 digenous on certain of our native species of Prunus, the remedy is obvious. Wlicn a 

 knot makes its appearance, the branch should be cut olf a short distance below the 

 slight swelling of the stem, which is found just below the knot. ' When cut off tljo 

 branches should be burnt to prevent the spores from spreading the disease ; for, al- 

 though the asci have but begun to form when the branch is cut off, they will grow 

 and ripen their spores even v/hen separated from the trees, as we know from experi- 

 ence. The question arises as to the best time for cutting off the diseased branches, 



*Agri. Kept, for 1861, p. 498. 



t See article by Col. Ales. Pearson in the present report. 



t Bulletin of the Bassey Institution, vol. 1. 



