54 PROCEEDINGS OF THE AMERICAN ACADEMY 



division fails to take place in some of the cells, and leaves a conspicu- 

 ously long and ill-sliapen cell, which, however, continues its growth 

 like the others. At the time of the most rapid growth the formation 

 of the walls follows so quickly on one another that the newly furmed 

 cells do not reach their full size before they divide again. As a con- 

 sequence of this the outer portion of an actively growing frond is 

 made up of groups of small, closely compacted cells, each group 

 having originated from the division of a single terminal cell (Fig- o). 

 The cells of these groups gradually grow and assume the normal 

 appearance, the outer ones continuing to divide, though more slowly 

 than before, and the inner ones losing themselves in the inner mass of 

 the frond. The activity of the terminal cells almost enin-eiy ceases 

 as the frond approaches maturity, and in the adult frond there is no 

 sign of turtlier growth. 



The tetrasporic fruit of Choreocolax was, as has been said at the 

 beginning of this paper, first mentioned by Farlow, who gives a brief 

 account of it. The tetrasporic fronds were not uncommon in the 

 material I collected at Nahant, and material was easily found from 

 which to study them. They were no more frequent at one time than 

 at anolhei", during the portion of the year in which I looked for 

 them. Externally, the tetrasporic plants present no characters by 

 which they may be invariably distinguished from sterile specimens. 

 The size of the frond bears very little relation to tlie presence of even 

 mature tetraspores, for it is not at all unusual to find in a very minute 

 frond not a millimeter m diameter tetraspores which are to all ap- 

 pearance perfectly developed. A vertical section of one of the 

 hemispherical swellings shows the tetraspores to be located on the 

 extreme periphery of the frond (Fig. 8). There is no definite limit 

 to the number of tetraspores to be found in a single specimen ; some- 

 times there are very few of them, while at other times there are so 

 many that they have quite crowded the terminal cells out of place. 

 All stages of growth of the tetraspores are present in one frond at 

 the same time, so that their development is not hard to trace. They 

 arise from the enlargement of certain of the terminal cells, but there is 

 no criterion by which it is possible to tell what ones will develop into 

 tetraspores. The first indication is a slight swelling of those cells 

 which are to form the spores (Fig. 9). They rapidly increase in size, 

 the contents of the transforming cells at the same time taking on a 

 more granular appearance than their unmodified neighbors (Fig. 10). 

 After the single cell has attained almost the size of the mature spore, 

 a transverse wall is formed across it (Fig. 11), and is soon followed 



