1008 MINNESOTA BOTANICAL STUDIES. 



garded as relatively new, while that in which the blocks are 

 smaller and the humus content greater, may be considered as 

 of greater age. This is not always the case. It happens 

 sometimes that talus falling from granite or other ledges of re- 

 sistant rock, lies along the shore in such a position that the 

 water laps among the fragments, carrying away much of the 

 organic material which might temporarily accumulate, and 

 thus for a very long time the blocks remain with the look of 

 new talus except for the development of lichens in luxuriance 

 on the fragmented faces of the rock. The different types of 

 talus that have been observed may be noted in their order. 



Coarse talus. This is of two classes, new talus, and old talus. 

 The coarse new talus is known by the scanty development of 

 lichens on the rock surfaces of fragmentation, the coarse old 

 talus by the disappearance of distinction between block-surfa- 

 ces originally exposed and surfaces exposed by the fracture. 

 A number of types of plant societies may be observed upon 

 such areas. If the blocks are very large and creviced the dis- 

 tribution is the same as that yet to be described under the head 

 of rock shores. Disregarding such a condition one may indi- 

 cate the following special formations. 



I. Thallophytic talus formations. The blocks are not strongly 

 creviced and the only plants able to gain a foothold are the 

 lichens and algae. Such formations are the first to appear on 

 new talus blocks, unless conditions of drainage and silt-deposi- 

 tion complicate the matter. They may also characterize old 

 talus-block surfaces when the shape of the fragment is unfav- 

 orable for soil accumulation. The character of the plants and 

 their relative abundance vary with the exposure of the surface, 

 one being lighter, warmer, more sheltered from the^wind than 

 another. 



II. Archegoniate talus formations. The characteristic plants 

 are mosses and ferns. The blocks that show this type of plant 

 population are generally along quieter shores where high 

 winds and surf are not troublesome. If the block be not too 

 large it may become covered down to high water mark with 

 luxuriant'growths of Hypnaceae and Polypodium, to the almost 

 complete exclusion of other plants. If, however, the block be 

 of sufficient size and proper inclination and surface contour to 

 permit the^accumulation of a soil, it may harbor many small 

 lithophytic flowering plants, and as the block grows older per- 

 haps even shrubby or arboreal vegetation may be established 

 upon its slowly gathered superficial coating of soil. 



