igi6] ROE—SPLACBNIDIVM 403 



Some of the hairs, as in Fucus, are shed later and the lining 

 cells put forth new papillate growths which elongate into sacs 

 (fig. 22) which are ultimately filled with spherical bodies ("fig. 24), 

 variously described as zoospores (10, 11) and gametes. Agardh (i), 

 Harvey (4), Hooker (5), and Laing (8) all describe Splachnidium 

 as dioecious, although no one of these authors reports having 

 actually observed antheridia. Laing speaks of oogonia "obscurely 

 pedicelled," developed from the lining of the conceptacle, each 

 oogonium giving rise "to a large number of oospheres, thus differing 

 from all other Fucaceae that have hitherto been described. Each 

 oosphere is very small, compared with the oospheres of other Fuca- 

 ceae." In another paragraph he states that "as antheridia have 

 never been observed it. is just possible that these hairs [apical 

 hairs] may be antheridial in function." The writer's feeling is that 

 the reproductive sacs contain isogamous gametes. However that 

 may be, the conceptacles, at the time the reproductive bodies are 

 ready for discharge, still contain the "initial" as a conspicuous 

 feature (fig. 23). 



Discussion 



Murray (ii, 12) and also Mitchell and Whitting (10) speak 

 of the "modified cell" of Splachnidium as homologous with the 

 "initial" of Fucus; and yet these same authors make this "unique 

 cell" one of the reasons for separating Splachnidium from other 

 families. The similarity holds true only in so far as the con- 

 ceptacle is concerned, where, as previously shown by the writer 

 (14), the conceptacle in each genus is the result of arrested develop- 

 ment and partial breaking down of a portion of the external layer 

 of the thallus followed by great activity of abutting tissue. The 

 initial row is in no way comparable to the true apical cell of 

 Fucus, segments of which are the basis of all tissue of the 

 thallus. 



The fact I ha I the initial row of Splachnidium occurs wherever there 

 is great activity is additional evidence for the simple origin of the con- 

 ceptacle. Splachnidium is a particularly favorable plant for study 

 along this line, since the same structure accompanies ordinary 

 vegetative growth as well as reproductive activity. 



