142 



by him in Gustine Lake, Fairmount Park. Upon examination, 

 this proved to consist of almost pure felted masses of Triboncma 

 bombyciniim. 



Having determined the plants which enter into the composition 

 of the algal paper mentioned above, it is important to describe 

 the method of its formation. All of the forms of algae mentioned 

 above are free-floating kinds ordinarily described as freshwater 

 plankton. When floating on the surface, such plants are driven 

 about by the wind that blows over the surface of the lake or 

 pond. Smaller masses of floating algae are blown together until 

 large mats are formed, in which dead leaves and other material 

 may be incorporated, and these mats may be blown to the shore 

 and anchored by drifting into shallow water. If such rafts of 

 material occur in a reservoir, as at Honey Brook, the drawing off 

 of the water would cause the stranding of the rafts. The water 

 held in suspension in the interstices of the filaments evaporates 

 and the cells dry up and extensive sheets of algal paper are thus 

 formed. In the case of algal rafts stranded on the shores of 

 ponds and lakes, the advent of hot weather and the lowering of 

 the general level of the water by evaporation would cause in a 

 similar manner the formation of the algal paper, or felt. 



The composition of this paper depends on the algae which are 



present in the pond when the formation of the paper begins. 



The paper may consist entirely of one plant, as in the diatom- 



aceous and oedogonial papers, or in a mixture of a number of 



diverse types of green algae with diatomaceous frustules and 



the remains of leaves blown into the pond from bordering 



forest trees. 



University of Pennsylvania. 



SHORTER NOTES 

 The Taxonomy of a Leaf-Spot Fungus of the Apple and 

 OTHER Fruit-Trees. — The "brown-spot" disease of apple 

 leaves was doubtfully attributed to the fungus Phyllosticta pirina 

 Sacc. by Alwood * in 1892. The same fungus occurs on the 

 leaves of pear, quince, and plum, and the disease is known by 

 the name of "leaf-spot," "frog-eye," etc. 



*Alvvood, W. B. Va. Agr. Exp. Sta. Bull. 17 : 62. 1892. 



