OP ARTS AND SCIENCES. 



187 



As can be seen from the above table, which represent specimens 

 taken at random, all the plants of this collection are remarkably long 

 ami narrow. The blade of No. 1 was broken off short, as if by 

 some accident. The tips of the rest were eroded in the customary 

 fashion. Nos. 1 to 9 were found growing in a .shallow pool just 

 above low-water mark, while 10 and 11 were found cast ashore on a 

 small beach not far away. All of them were of a remarkably light 

 yellow-brown color, and very pellucid for specimens so long as some 

 of them were. About thirty specimens of much the same character 

 were collected at this locality on the same date. All sorts of transi- 

 tions between this narrow form and the more ordinary form are 

 found. I have seen plants of this narrow form at Nahant and Marble- 

 head also, but they were few or single, and this is the only time that 

 I ever found so many together. 



Fourth Period. — 1. Transitional Forms. — Some specimens were 

 collected at Nahant, June 12, 1889, which show some very striking 

 peculiarities. The specimens, between twenty and thirty of which 

 were carefully examined at the time, were all about the same size, 

 and apparently of about the same age. They grew not only just 

 below low-water mark, but in the highest pools as well. They were 

 all in the neighborhood of 55 cm, long. The holdfast was well de- 

 veloped, and the hapteres were stout and of a dark brown color. The 

 stipe was decidedly flattened above, and from 6 to 10 cm. long. At the 

 top where it passes over into the blade there is a noticeable ridge 

 made by the abrupt transition from the thick stipe to the much thinner 

 blade. The stipe has become a very dark brown, and is opaque, hav- 

 ing lost entirely the translucent appearance characteristic of the organs 

 of the younger plant. But the most noticeable and interesting change 

 is one which is to be seen in the blade itself. In the upper part of 

 this the color is still decidedly yellowish, and the cryptostomata are 

 abundant and conspicuous ; but toward the ba.se there is a noticeable 

 transverse constriction (cf. Fig. 11, A), and below this the blade is of 

 a dark brown, agreeing more nearly with the stipe in color, and almost 

 if not entirely destitute of cryptostomata. Tlie cryptostomata grow 

 smaller and smaller as they approach the constriction and disappear at 



