SCHISTOSTEGA OSMVNDACEA MOHR. 367 



they are so to a very much less extent. I have colonies of Schis- 

 tostega growing in captivity from various localities on Dartmoor 

 which rather confirm this view ; they are kept quite separate and 

 are all extremely healthy and vigorous. One colony is, and has 

 been since it was first collected, quite barren, but produces an 

 abundance of gemmae ; another in the spring of 1917 was covered 

 with capsules and at the present time is again covered with ripening 

 capsules, but gemmae are very infrequent. Such a correlation is 

 repeatedly met with among mosses, as for instance the deciduous 

 leaves in barren states of Campylopus pyriformis, Brid., which 

 condition is scarcely developed when the plant is fertile. These 

 gemmae are multicellular, club-shaped bodies of about 100/x in 

 length produced from the distal end of a filament of the protonema 

 by a cell becoming enlarged and ultimately separating itself 

 from the parent cell by the development of a separation cell 

 (Plate 23, fig. 5). A new protonema may be produced by budding 

 from one of the cells of the gemma (Plate 23, figs. 6, 7) ; or in 

 rare instances the gemma may produce another gemma without 

 the production of protonemal growth (Plate 23, fig. 8). These 

 gemmae secrete a material of great adhesive power by which they 

 become attached so firmly to foreign bodies that some force is 

 necessary to dislodge them. Apparently the mucilage is excreted 

 by the cells at the distal end of the gemma, as I have never seen 

 one affixed by any other part of the bud. Yates has called atten- 

 tion to a similar phenomenon among the Hepaticae (17). 



It is the protonema of Schistostega that gives it the great 

 interest it possesses for the biologist, and which is probably unique 

 in the vegetable world in its highly developed system of photo- 

 synthetic cells. Bowman quite early in the history of the plant 

 gave a description of the convex light-cells and their function (18) , 

 and of late years much work has been done on them principally by 

 Noll (19) and Vuillemin (20) . The protonema is generally regarded 

 as persistent, unlike the majority of mosses in which it disappears 

 on the establishment of the plant, but I do not think that it can 

 be regarded as essential to the life of the adult plant, for in those 

 colonies I have growing in confinement it is reduced almost to 

 extinction when the plants are full grown. One has to remember 

 that a patch of Schistostega usually contains all stages of growth 

 simultaneously, and my examination of such patches leads me to 

 ^»7fer that it is the younger portions of the colony that produce 



