1 82 ANATOMY OF THE GYMNOSPERMS 



20 C. ; maximum, 40 C. The relation of moisture and heat 

 to continued life conforms to the same principle as stated 

 for the bacilli, namely, that the spores of Penicillium glaucum 

 and Rhizopus nigricans rarely germinate if exposed for one or 

 two hours to air which has been heated to a temperature of 70 

 to 80 C., while they are entirely destroyed at 82 to 84 C. On 

 the other hand, spores which have been heated in their own 

 nutrient fluids to a temperature of 54 or 55 C. completely 

 lose all power of germination (84, 725). 



Although but little is as yet known respecting the life history 

 of the fungi, and especially the particular conditions under which 

 the germination of the spores occurs, the foregoing facts direct 

 attention to the great diversity and wide range of the conditions 

 involved for different species. Fortunately the researches of 

 Hartig have made it possible to gain an insight of a more exact 

 character into the operations of one of the most destructive fungi 

 known, the dry rot (Merulius lachrymans), a short account of 

 which may serve as a working basis for all fungi. 



The spores of dry rot germinate on the surface of damp 

 timber, and the growing plant quickly penetrates the tissue ; 

 but the germination of the spores demands certain conditions 

 which are fulfilled by the presence of alkaline products, particu- 

 larly those which are ammoniacal. It will therefore be found 

 that locations where there is bad drainage, especially in cellars 

 and stables where ammoniacal products are likely to be abun- 

 dant, offer exceptionally favorable situations for its development. 

 When the plant has once entered upon its course of growth its 

 extension is very rapid, and it thrives wherever the air is con- 

 fined, warm, and damp, though it is well known that air, i.e. 

 air which is freely circulating and which contains a much lower 

 percentage of moisture, will cause the death of the plant in one 

 or two days, except in deeply seated parts. From this point 

 of view it may be observed that the disease is readily propa- 

 gated in badly ventilated cellars or in confined areas where air 

 does not freely circulate and there is a tendency to the collec- 

 tion of moisture. Thus in the construction of the MacDonald 



