AUTOBASIDIOMYCETES 457 



The flesh is white and soft when young, becoming tough with age. 

 Nevertheless, this sporophore persists but a single season, while a 

 diseased tree may continue to produce sporophores throughout a 

 period of years, and even for some time after having been felled. 



In the development of the sporophore a knob-shaped, fleshy body 

 appears, from which may arise one or more short stems, and the 

 changes in one of the latter are usually about as follows : An apical 

 depression is the first evidence of the pileus. Further growth in 

 the stem is hyponastic, raising the depression toward the horizontal, 

 and at the same time there is rapid and distinctly one-sided lateral 

 expansion, and later, thickening in the region of the depression, 

 so that it becomes a definite pileus, with the greatest growth on the 

 sides farthest from the axis of attachment, thus eventually giving 

 the excentric or almost lateral type of sporophore. 



The hymenium is very early differentiated, first as very shallow 

 reticulations, but a downward growth of the netted ridges develops 

 in time the relatively deep pores of the mature sporophore (Fig. 223). 

 The basidia and spores are not unusual in form. The latter measure 

 about 1 2 x 5 p. It is not without interest to note that the spores 

 are forcibly thrown from the sterigmata in this species, and doubt- 

 less in practically all other species of Basidiomycetes, the form of 

 the sterigmata and the attachment of the spores to these frequently 

 suggesting the possibility of well-regulated .tensions. By a com- 

 paratively accurate method Buller estimated the number of spores 

 produced in a single pore, and found it to be about one million, 

 seven hundred thousand. The spores, like those of mold fungi, 

 will withstand immersion in water for a long period. 



VII. DECAY, OR BROWN ROT, OF TREES 

 Polyporus sulphureus (Bull.) Fr. 



ATKINSON, GEO. F. Studies of Some Shade Tree and Timber Destroying 

 Fungi. Cornell Agl. Exp. Sta. Built. 193: 208-214. 1901. 



SCHRENK, H. VON. Polyporus sulfureus (Bull.) Fr. Div. \Vg. Phys. and Path., 

 U. S. Dept. Agl. 25: 40-52. pis. n (in part), /j. 1900. 



The sporophores of no other fungus present, probably, a more 

 striking appearance than the fresh, vigorous, sulfur-yellow cluster 

 of the above species. It cannot be considered a very virulent 

 disease-producing organism, in spite of its wide distribution and 



