36 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



the waves, and by friction upon other algae and upon rocks. 

 The portions thus reduced persist for a considerable time 

 and give rise to numerous proliferations which exhibit all 

 the characters of the original frond. 



It seems strongly probable that the remarkable degree of 

 variation in the shape and position of the sori in N. 

 ruprechtianuni has been a fruitful source of error to those 

 who have been called upon to identify the forms belonging 

 to this species. It is difficult, perhaps, without extensive 

 examination of plants on the shore at all seasons, to realize 

 what a diversity of form may be found within the specific 

 limits. Especially is this diversity important in considering 

 the sori, which are usually much employed in establishing 

 specific distinctions. 



The examination of abundant material of JV. ruprecht- 

 ianuni has shown that the plants fall into three groups dis- 

 tinguished by the differences in the method of production 

 of the sori, without regard to other features. In one group 

 the sori are produced on the upper, flabellately expanded 

 segments of the frond, and are arranged in rather wide 

 linear sori, or lines, distinct or occasionally confluent, and ex- 

 tending in a more or less connected fashion from the median 

 portion of the segment to the margin. A second group 

 exhibits these linear sori usually confined, however, to the 

 apices of the segments, while along the margin are pro- 

 duced numerous minute proliferations upon which are borne 

 sori having the form of rounded patches. In a third group, 

 the sori are confined to the marginal proliferations or to the 

 similar proliferations appearing upon both the margin and 

 the surface. While, in general, these variations in the posi- 

 tion and shape of the sori are seen on different plants, yet 

 it is of great importance in employing them as specific char- 

 acters to keep in mind the fact that these three different 

 dispositions of the sori are likewise found on one and the 

 same plant. 



A similar habit with respect to the production of sori is 

 seen in JSf. violaceum, where, however, the linear sori are 

 much narrower and the marginal ones are often widely 



