Take-all and White-heads in, Wheat. 417 



Maiigin (19) in France, had already sown the spores of this fungus 

 upon young wheat-i)lants, and infected them successfully as early as 

 1899/ 



Nature of the Fungus. 



Having settled the fungus ox'igin of the disease, the next step is 

 to study the fungus itself, so that we may know how it lives and 

 grows and multiplies, and knowing something of its nature to fight it 

 with suitable weapons. 1 have no intention of giving a detailed 

 account of it here, but just sufficient to enable us to understand, the 

 reason for the treatment recommended, aided by the illustrations 

 prepared from photo-micrographs made by my assistant. 



Every fungus consists of a vegetative portion, which is usually 

 composed of innumerable, interlacing, fine threads, more or less 

 closely knit together, and collectively known as mycelium or spawn, 

 and a reproductive portion for propagating the species. The vegeta- 

 tive ])ortion, or mycelium, as it is called, may exist in three or four 

 different forms. First, there is the kind consisting of numerous dark- 

 brown, somewhat interlacing filaments, spreading upwards from the 

 root, as shewn in Figs. 3 and 7, magnified 200 times, and Fig. 8, 

 magnified 400 times. Indications point to a spread of the fungus 

 from one root to another by this mycelium, as long strands are often 

 found piercing the roots and joined to the form shewn in Fig. 6 

 (x 200), which fills the cells of the roots and stem, causing the dark- 

 brown or black appearance. Then there is what is termed the plate 

 mycelium, seen in Fig. 5 (x 200), which occurs almost exclusively 

 between the inner sheath and the stem, and which is found to be 

 connected with the forms previously described. This plate mycelium 

 is as a rule easily peeled off from the stem, and in fact when the plants 

 are dry it naturally comes off' in fiakes, and very probably may serve 

 to infect young plants the succeeding year. Then in Fig. 4 (x 200) 

 is shewn what is really a modification of the form in Fig. o, many 

 light-brown strands being joined together to form a broad band, 

 which passes upwards on the inside of the sheath. All these forms 

 draw nourishment from the wheat-plant and appro])riate it for the 

 ultimate purpose of forming the fruiting portions or perithecia. The 

 perithecia or spore-cases are fiask-shaped bodies, of which the lower 

 swollen part is immersed in the tissues of the wheat plant, and the 

 neck, which may be straight, but is usually slightly curved, projects 

 from the surface. (See Fig. 2 natural size. Figs. 9 and 10 magnified 

 three times. Fig. 11 fifteen times, and Figs. 12 and lo thirty times.) 

 They are either scattered or in grou})S, and may occur on the roots or 

 on the sheath. Inside each spore-case are numerous little sacs or 

 asci (Fig. 14, x 400) each of which contains eight spores (Figs. 15 

 and 16, x 400) so that a single spore-case contains an immense 

 number of spores. When the spore-cases are mature the little sacs 

 are expelled one after another at the mouth, and the spores are set 

 free in the presence of moisture. 



The spores themselves are elongated slender bodies, divided into 

 compartments by cross-partitions, as shewn in Figs. 15 and 16. They 



