THE SECRETARY'S PORTFOLIO. 341 



curl, potato rot, wheat rust, and a long list of other microscopic plants too 

 small to be seen except by their destructive effects as they prey upon the higher 

 forms of vegetation. The fungus or parasitic plant was first described in 1838, 

 but it remained for Dr. Farlow of Harvard university, to publish a full account 

 of the m'nute plant and its methods of propagation and growth. Quoting 

 from Dr. Farlow he gives this argument against the theory that the disease is 

 caused by insects: 



First the knots do not resemble the galls made by any known insects. Sec- 

 ondly, although insects, or remains of insects are generally found in old knots, 

 in most cases no insects at all arc found in them when young. Thirdly, the 

 insects that have been found by entomologists in the knots are not all of one 

 species, but of several different species, which are also found on trees that are 

 never affected by the knot. On the other hand, we never have the black knot 

 without the Sphwria morbosa (the scientific name of the fungus), and the 

 mycelium of that fungus is found in the slightly swollen stem long before any- 

 thing that could be called a knot has made its appearance on the branch, and 

 furthermore is not known to occur anywhere except in connection with the 

 knots. 



He gives the the following facts concerning the disease and its remedy : 



The knots range in size from an inch to a foot in length, usually growing 

 upon one side of the branch, causing it to bend away from that side, or twist 

 irregularly. The parasite first makes its appearance in the spring, when the 

 affected branch increases rapidly in size and becomes soft in texture. The bark 

 is soon ruptured in various places and the soft interior comes to the surface, 

 expands rapidly, and soon turns green. Multitudes of minute spores are 

 formed on this exposed green surface, which fall away and are carried by the 

 winds, etc., to other twigs, thus propagating the disease. These spores continue 

 to be formed until late autumn, when the surface of the knot takes on a dry 

 and black surface. In the meantime insects may have taken possession of the 

 soft tissue within and so eaten and destroyed it that at the end of the season 

 only a thick, hard crust, or shell, remains. Another kind of spore is found in 

 small pits and sacks of the crust, and as they form late in autumn they are the 

 winter spores of the fungus and the form in which the pest is carried through 

 the winter. These spores germinate in the spring and thus continue the black 

 knot. The same knot lasts for several years, or until tlie branch is killed, it 

 spreading from the old growth up and down the branch. 



The only remedy is the knife. A branch once affected is beyond recovery, 

 and as long as it remains is a seat of propagation of the spores of the fungus. 

 The knots should be cut off some inches below the main part, because the 

 wood for some distance is filled with the threads of the fungus. I have seen 

 cases where the knot was thought to be entirely removed by the knife and a 

 new one would form at the cut end of the stump, thus showing that the work 

 was not properly done. The removed branches should all be burned, as the 

 knots contain spores which will otherwise become detached and spread the dis- 

 ease. The best time to cut the knots is in late autumn, because the leaves 

 having fallen the excrescences can be more easily seen. 



RASPBERRY RUST. 



A correspondent of the Fruit Recorder says that the first visible indications 

 of rust upon raspberries are a slender growth of the young canes, and in plants 



