46 Rhodora (Marcu 
geneous materials, — in fact little more than a loosely-matted collec- 
tion of flotsam hardly brought to a true ball by wave-action, 
There remain to add a few facts about vegetable balls of a totally 
different morphological origin, of which three distinct kinds are 
known to me. First, there are the photo-bezoars, mentioned occa- 
sionally in botanical literature, which are formed of matted grass- 
awns, cactus-bristles, etc. in the stomachs of herbivorous animals. 
Second, the letter in Science, above mentioned, was followed by two- 
others in later numbers of that journal (XIX, 926 and XX, 86) by 
J. Adams of the Royal College of Science of Dublin, giving refer- 
ences to balls formed by the alga Cladophora in Scottish and Danish 
Lakes. I am informed, however, by Professor F. E. Lloyd and by 
Dr. M. A. Howe, that the balls formed by these Algae, of which there 
are specimens in the Museum of the New York Botanical Garden, 
are of a character quite different from that of the ones we are here 
considering, for the balls of Cladophora are the result of the normal 
mode of growth of the plant, and are not simply mechanically-pro- 
duced aggregations, 7Z/ird, Mr. John H. Sears, of the Peabody 
Museum at Salem, Mass., writes me (Feb. 9, 1905) that he finds on 
Ipswich and other beaches a kind of vegetable ball, or “pebble,” 
formed from the matted sods of Juncus Gerardi, or Black Grass, 
thrown upon beaches in ditching operations. ‘These sods are rolled 
about, worn down and rounded by action of the waves; and they may 
in addition pick up in the process various other materials, — grass 
fragments, bits of wood, fish-bones and even sand. Obviously such 
balls are very different in origin from those of the fresh-water ponds. 
Mr. Sears also adds that he has found vegetable balls on the shores 
of Wenham Lake. 
There are, therefore, at least four morphologically distinct modes 
of origin for balls of vegetable matter, and very likely there are also 
others. : 
Returning for a moment to the particular kind here under con- 
sideration, it seems plain from the descriptions cited that they are 
simply an incidental mechanical result of the rolling about of light 
water-logged materials on sandy bottoms by the under-water parts of 
waves, aided perhaps as to their cohesion by the development of 
glutinous micro-organisms. On this basis the balls ought to occur 
wherever this combination of conditions is found, and hence in some 
parts of most shallow sandy-bottomed lakes; and it is surprising that 
