224 THE PLANT WORLD 



Briefer Articles. 



GEOTROPISM OF POLYPORUS. 



While wandering on Mount Sunapee, N. H., my attention was 

 attracted by a prostrate log with several large bracket-fungi, Polyposis, 

 upon it. Not being a student of the fungi, I do not know the species, 

 but can only say that it was one of the familiar woody ones with the 

 lower surface marked with small, dot-like pores. They form " brackets " 

 upon trees, and are often collected by " summer boarders," who draw 

 landscapes of doubtful beauty upon the white under-surface by means 

 of a pin or pointed stick. 



These fungi are perennials and last for several years. The first season 

 they are not more than two or three inches across. The next year a new 

 spore-bearing layer grows over the one of the preceding season, but this 

 time it is considerably larger. In succeeding years the process is repeated, 

 so that the bracket grows downward and outward from the original point 

 of attachment to the tree trunk. The growth of the spore-bearing layer 

 is evidently " geotropic " ; that is, it is influenced by the earth's attrac- 

 tion in the same way that roots grow downward. When viewed from 

 above the only white that can be seen is a narrow rim around the edge 

 of the bracket. The advantage of having the spore-bearing layer on the 

 under-surface is obvious. If the tiny pores were directed upward the 

 first rain or heavy dew would fill them with water, which would be very 

 slow in evaporating. The chances are that the spores would suffer and 

 perhaps decay. Besides this the pores would be sure to become filled 

 with dust that would prevent the escape of the spores. 



This geotropism had never been brought to my attention until I saw 

 the log mentioned above. When the tree was erect the fungi grew on it 

 for several years, as could be seen by making a section of a bracket and 

 counting the .spore-bearing layers. The fall of the tree did not kill the 

 fungi, but it did put them in an awkward position on edge, instead of 

 horizontal. The first season a new growth started on the face of the 

 bracket, about opposite the point of attachment to the trunk of the tree, 

 and true to its tendencies, it took a horizontal position, at right angles to 

 the original growth. The next year, 1903, a new layer was formed in 

 the usual way on the one preceding. In addition to these springing from 

 the centers of several of the brackets, there were some smaller outgrowths 

 from other parts of the original ones, thus giving a sort of terraced effect. 



More than once I have seen other woody fungi that had a spore- 

 bearing layer upon what was at first the upper surface. In these cases 

 the log or stick on which they grew had rolled over and inverted them. 



C. E. Waters. 



