488 EXPERIMENTAL FARMS 



4 GEORGE V., A. 1914 



ERGOT. 

 Claviceps purpurea (Fr) Tul. 



* 



This fungus (together with one or two closely-related specimens which for our 

 purpose need not be distinguished from it), is of importance to the agriculturist, not 

 so much because it causes injury to the plants on which it grows, but because the 

 resting bodies, or ' ergots,' contain substances highly injurious to the health of animals. 



If a careful examination be made in late summer or fall of the 

 cars of rye, wheat or barley, or of many grasses, e.g.,. couch, particularly 

 if these are growing in damp situations, it may be noticed that in 

 some of the florets the ' seed ' is replaced by a spur-like or rounded, 

 hard, purplish body, which is much larger than the grain would be, and consequently 

 projects beyond the chaffy scales of the ear. These bodies are masses of resting 

 mycelium (sclerotia) of the fungus and are known commonly as ' ergots.' In size 

 they vary according to the plant on which they occur, reaching a length of an inch or 

 more on rye and being very small on such a grass as red top (Agrostis). Many species 

 of grasses are liable to be attacked, whilst among cereals rye is most commonly affected, 

 and to a less degree, wheat and barley. Unless harvested with the host plant, the 

 sclerotia finally drop off and fall to the ground. Such of these as have been subjected 

 to the right conditions undergo a new development in the following spring or early 

 summer. From each, one to several rather stout stalks grow up into the air, reaching 

 perhaps a length of an inch or more, each stalk terminating in a rounded purplish 

 'head' (stroma), whose surface is roughened with numerous small projections. These 

 projections terminate in minute openings, each communicating Avith a separate 

 chamber or cavity (perithecium) in the ' head.' At the base of each cavity is a dense 

 •tuft of elongated, somewhat club-shaped, spore-sacs (asci) in each of which eight 

 threadlike spores are found. Ultimately these spores are liberated from the sacs 

 enclosing them, and forced out through the opening of the perithecium into the air, 

 to be dispersed by the wind. Should one of these spores be carried into the open 

 flower of a susceptible grass or cereal and reach the ovary it is capable of producing 

 a mycelium which develops in and around the ovary and which gives rise externally 

 1c large numbers of minute spores (conidia) together with a sweet, sticky liquid. The 

 latter attracts certain insects to which the conidia adhere and are thus carried to 

 other flowers. Each conidium is able to reproduce this stage of the disease, should it 

 be brought into contact with the ovary of a- susceptible plant at the right stage of 

 development. This phase of the life-history of the fungus is so unlike the ' ergot ' 

 and the structures developed from it, that before the full life-history had been followed 

 it was considered as belonging to a distinct species of fungus and given the generic 

 name Sphacelia. It is still referred to as the Sphacelia or sphacelial stage. The 

 mycelium, however, still continues to increase in quantity and becomes con- 

 tracted, forming a mass replacing the ovary, but to the tip of which the 

 withered-up stigmas and upper part of the ovary remain attached for some time. 

 Conidia are no longer produced, and the outer layers of mycelium develop into a com- 

 paratively hard protective layer, the outer walls of which assume a dark purplish 

 colour. This is now the sclerotium or ' ergot ' stage similar to that with which we 

 started. 



The conditions which determine the germination of the sclerotia have not yet been 

 fully determined, but apparently one very important factor is the degree of ' drying- 

 out' to which they have been subjected. A completely dried-out sclerotium is com- 

 monly believed to be incapable of germination. Hence sclerotia a year or more old 

 rarely germinate, while those kept even for a few months under ordinary warm con- 



