SEED IMPROVEMENT MEETING. 20/ 



saturated atmosphere is necessary if the spores are to germi- 

 nate. Some soil fungi, hke the potato scab organism, require 

 an alkahne condition and the addition of acid pliosphate to 

 the soil is decidedly detrimental to them, v\diile others require 

 an acid condition for their best growth. It may be said with 

 due emphasis that whatever tends to remove or to diminish 

 the conditions favorable for fungus attack will prevent or 

 decrease infection from those organisms. 



Not all fungi affect their host plant to the same extent. The 

 seed fungus of Lolium passes its entire existence within the 

 host plant without causing injury to the host, indeed stimulating 

 it if anything, to increased growth. The rusts seldom cause 

 serious injury to their host at first, though later when their 

 development is nearing completion they may cause a great 

 reduction in yield and may even injure the host to such an 

 extent that no seed is produced. This ability of the rusts to 

 live within the host without causing injury is of great advantage 

 to the fungus as it is not able to extract its food from dead 

 tissue. Many lower fungi, as those causing damping off of 

 seedlings kill outright the tissues they attack. Such forms are 

 able to pass a portion of their existence as saprophytes, and 

 ■certain fungi, ordinarily saprophytes, may become parasitic, 

 as mentioned before, if conditions are particularly favorable. 

 These usually attack weakened or detached parts of plants, 

 such as the fruit, tubers, etc. Thus we find the common blue- 

 mould causing a rot of apples in storage and the bread-mould 

 rotting sweet potatoes. 



Some fungi are cosmopolitan in their nature and may attack 

 many dift'erent kinds of plants, but most parasitic organisms 

 are more restricted in their range. Fire blight, a common and 

 destructive disease of pears, is confined to a few plants of the 

 rose family. The club root, a serious disease of cabbage and 

 turnips, and the white rust of crucifers occur on quite a large 

 number of species within the mustard family. The smuts are 

 extremely common on cereals and occur also on a few other 

 plants, but each species of smut occurs on a single host plant. 

 Compare the loose smut of wheat with the loose smut of barley. 

 Both occur at the flowering time of the grain affected ; both 

 ■completely destroy the inflorescence, reducing the head to a 

 •dusty mass of black spores ; they are similar in their develop- 



