DEPARTMENT OF AGRICULTURE. 



(c.) Bacteria. 



(d.) Insects. 



The only flowering plants of practical importance in this Province as parasites 

 of agricultural plants are the dodders, of which the most important are the alfalfa 

 and clover dodders. These will be found to be treated in some detail under " Clover." 



The lesions or structural alterations caused by many minute animal organisms, 

 such as eel-worins, pear-leaf blister-mite, and gall-insects, would naturally be included 

 in a study of plant-diseases. Since, however, control measures depend on a thorough 

 knowledge of the life-history of the parasite, such diseases, from the practical 

 economic standpoint, are usually relegated to the province of the^ entomologist. 



FUNGI. 



The fungi are a group of plants whose most constant and. superficially, most 

 striking character is the absence of the green colouring-matter (chlorophyll) found 

 in most plants. It is in virtue of this green colouring-matter that the typical plant 

 is able to build up the complex organic materials, such as proteids. starches, sugars, 

 etc., required for the nutrition both of the plants themselves and of animals, from 

 the simple mineral matters in the soil, water, and the gases of the atmosphere. 

 With rare exceptions, plants which do not possess chlorophyll are, like animals. - 

 dependent on organic food already manufactured. This they obtain in one of two 

 ways, namely : 



(1.) From living plants or animals, in which case they are said to be pa: 



(2.) From dead animal or vegetable matter, in which case they are said to be 

 saprophyte*. 



Good examples of saprophytic fungi are the common mushroom and the moulds 

 to be found only too often on bread, jam, etc. Saprophytic fungi and bacteria play 

 an important part in the economy of nature by getting rid of the dead bodies of 

 plants and animals through the processes of decay and putrefaction which they bring 

 about. The line between parasite and saprophyte is not very clearly drawn, however. 

 There are some fungi which, so far as is known, can only live as parasites of a living 

 plant, and there is a much more numerous group which do not appear to be able to 

 attack living organisms under any conditions. One of the difficulties of the grower 

 in combating plant-diseases, however, lies in the fact that an organism which causes 

 a serious disease may exist for a considerable time as a saprophyte on the decay ins 

 organic matter in the soil. Starving out such a parasite by rotation is thus rendered 

 difficult or impossible. On the other hand, a fungus normally a saprophyte may 

 become a parasite under altered conditions. Many fungi, for instance, which pro- 

 bably cannot attack a healthy plant, but which live perhaps on dead wood, can 

 establish themselves in wounds and spread from there into the adjacent healthy 

 tissue. 



The structure of a fungus is peculiar in being made up of threads, which usually 

 branch repeatedly. Each thread is termed a hypha; the network of threads engaged 

 in obtaining food, as contrasted with those set apart for purposes of reproduction, is 

 termed the mycelium. Even such complex structures as the ordinary mushroom, or 

 the hard woody polypore* or bracket-fungi, are made up of closely interwoven, and 

 often hardened, hj/phee. In the case of parasitic fuugi the hypha? may be mainly 

 external, sending out little feeding processes between the superficial cells to absorb 

 nutriment from them. This is the case with most powdery mildews. In other cases 

 the hypha; penetrate the tissues of the host (as the attacked plant is termed), passing 

 in between the cells and often entering them or sending out special feeding processes 

 (haustoria) into them. In many cases the hypha? secrete substances which kill the 

 cells bodily, after which thftir contents are used as food. The late-blight fungus of 

 the potato is a good example. In others the fungus stimulates the cells of the host 

 to increased division and growth, so that enlargements or tumours result ; e.g.. many 

 rusts, club-root of crucifers. 



