134 The Ottawa Naturalist [Dec. 



spores are produced in concept acles, which are exceedingly well 

 protected. They adhere firmly to the substratum on which 

 they have been produced or are imbedded therein. 



Our next problem to consider is the mode of life of fungi 

 and their influence upon the host plant. 



Green plants or chlorophyll-bearing plants manufacture 

 their food, as you know, from the carbonic acid of the air by 

 means of the small chlorophyll grains in their leaves and by the 

 action of sun and water. This physiological process is known 

 as "assimilation." The first visible product of assimilation is 

 starch. The starch again undergoes certain changes and forms 

 carbohydrates like dextrose and sugar, which are used as food 

 by the plants. In other words, the manufacture of food neces- 

 sary for the growth of the green plants takes place in the chloro- 

 phyll-bearing portions by means of this chlorophyll substance. 

 Fungi possess no chlorophyll. Hence, they are not able to 

 utilize directly the carbonic acid of the air. They are com- 

 pelled to search elsewhere for the carbohydrates essential for 

 their development and accomplish this by living upon substrata 

 from which they are able 1 o obtain a "ready-made" supply of 

 food. Parasitic fungi live upon plants in various ways. They 

 may be confined to the surface entirely like the mildew fungi, 

 when there will be produced on the mycelium peculiar sucker- 

 like organs so-called haustcria by which they absorb their 

 food from underlying cells. Other fungi, by far the greatest 

 number, live within the tissues of the host plant. They may also 

 produce haustoria, but more generally the absorption of food 

 takes place directly by the action of the vegetative hyphae 

 on the infected tissues. 



Following the growth and development of parasitic fungi, 

 a collapse of these cells, robbed of their contents, takes place 

 and the earliest symptoms of disease appear. Often the infec- 

 tion is exceedingly local and the result is the production of smaller 

 or larger spots of dead tissue. The shot hole fungi of plums, 

 cherries and peaches, illustrate well this peculiarly confined 

 growth. Quite recently my attention was called to the out- 

 break of an alarming disease among cherries in Prince Edward 

 Island. On investigating the epidemic I found that this trouble 

 was due to a common plum and cherry leaf spot fungus which 

 had defoliated practically all attacked trees. Two or three 

 years' repetition of this malady has resulted in the wholesale 

 destruction of cherries in this Province. 



Other fungi may attack, besides the leaves and fruit, the 

 young shoots of trees and destroy last year's growth and thus 

 much of the expected harvest. Others again, cause cankers 

 which spread from year to year until the whole branch is ringed 



