ig 1 7l DUNN—DUMONTIA 433 



Lewis (8) has shown that the sexual and asexual generations 

 in most of the Florideae at Woods Hole differ physiologically, but 

 are identical in vegetative structure, chromosome number of course 

 excepted. These two generations in many forms appear at dif- 

 ferent seasons and have a tendency to grow on different kinds of 

 substrata. The plants shown in figs. 2 and 5 are fair examples 

 of well developed cystocarpic and tetrasporic plants of Dumontia 

 filiformis. It is evident from a comparison of these plants that 

 in this species also the two generations are morphologically almost 

 identical. The tetrasporic and cystocarpic plants of Dumontia, so 

 far as substrata on which they grow are concerned, appear to be 

 physiologically identical also. The two kinds of plants grow 

 together on all the large rocks and in most of the tide pools. The 

 tetrasporic plants were more abundant on the whole than the 

 cystocarpic ones, and a few pools contained only the former. These 

 tide pools, however, were in every instance within 3 or 4 feet of 

 apparently similar pools on the same level, in which both kinds of 

 plants grew. The temperature of the water was taken in a number 

 of the pools. It was found that the temperature of pools in the 

 same vicinity did not vary more than 2 C. This difference 

 existed between pools which contained tetrasporic plants only, 

 as well as between these and those pools in which both kinds of 

 plants were present: 



SEASONAL OCCURRENCE 



Male and young female plants of Dumontia were collected in 

 the latter part of April 19 14 and on April 12, 191 5. An unsuccess- 

 ful search was made for plants in January 19 14. It is believed 

 that the plants were not then present. The ratio of female to male 

 plants in the collection made in April 19 14 could not be determined, 

 owing to the fact that the plants when examined were considerably 

 broken up. The ratio of female to male plants in the collection of 

 April 12, 191 5, was 3 to 1. This ratio is based upon the examination 

 of 24 plants collected from several different tide pools. Another 

 collection of plants was made on April 26, 191 5, and of these plants 

 24 were examined, all of which proved to be female. Of these 24 

 plants 10 bore only carpogonial and auxiliary cell branches, while 

 14 bore chiefly young cystocarps and auxiliary cell branches. 



