528 THE POPULAR SCIENCE MONTHLY. 



by rot, and that, within one year after the house was erected, all the 

 basement floor was in a state of premature decay. In cases of dry-rot, 

 where the mycelium passes through substances from the external sur- 

 face, it separates into innumerable small branches ; when it proceeds 

 from slime in the fissures of the earth, the mycelial fibers shoot in every 

 direction and are very much tangled. Arising from the roots of trees, 

 they look at first like hoar frost, but soon show regular toadstools. 

 When they grow in very damp situations, they feel fleshy and extend 

 equally around a circular space which they wholly cover unless obsta- 

 cles interpose. 



Excessive damp is unfavorable to this fungus, and its growth is 

 more rapid in proportion as the situation is less damp, until the proper 

 point for the growth of vegetation is reached. When the fungus ex- 

 tends to dry situations, its effects are more destructive to the timber 

 on which it grows : it is very fibrous, and in part covered with a light- 

 brown membrane perfectly soft and smooth. It is often of great mag- 

 nitude, projecting from the timber in a white spongeous excrescence, 

 on the surface of which a profuse humidity is frequently observed. 

 Sometimes it forms only a fibrous, thin- coated, irregular web on the 

 surface of the wood. Excrescences of a fungiform appearance are 

 often protruded amid those already described, and are evidences of a 

 very corrupt state at the spots whence they spring. Sometimes they 

 arise in several fungiforms, each above the other, without any distinc- 

 tion of stem ; and in some corrupt states the small acrid mushroom is 

 generated. 



But there are two or three species of fungi that are chiefly con- 

 cerned with the process of dry-rot. The Merulius lachrymans (often 

 called the dry-rot) is a most formidable enemy of timber. When the 

 section of a piece of wood attacked internally by dry-rot is examined 

 through a microscope, and minute white threads are seen interlaced 

 and matted together all through its substance, and when this cottony 

 texture effuses itself over the surface of the timber, and in the center 

 of it a gelatinous substance forms which gradually becomes tawny and 

 wrinkled and sheds a red powder on the white, downy surface, you 

 have the Merulius lachrymans. But, long before this last stage of 

 growth is reached, the interior of the wood has perished. As soon as 

 the cottony filaments are seen upon timber internally affected, we may 

 be sure that an apparently solid beam may be crumbled to dust be- 

 tween the fingers. In his botanical description of this plant, Dr. 

 Greville says it is " soft, tender, at first very light, cottony, and white ; 

 veins appear, at length, which are of a fine orange or reddish brown, 

 forming irregular folds, usually so arranged as to appear like pores, 

 but never anything like tubes, and, when perfect, distilling drops of 

 water." Hence the term lachrymans. The folds or pores here spoken 

 of are the reproductive portion of the plant. They are covered by the 

 hymenium or spore-bearing membrane, which sheds its red powder 



