2 4 o BOTANICAL GAZETTE [march 



claim that the conceptacle is merely a slight modification of the 

 original external layer of the thallus. 



Following segmentation of the apical cell, in Fucus, some 

 segment on the inner Up of the apical groove, close to the apical 

 cell itself, ceases activity, and through failure to continue growth 

 for a time is left in a depression by the active growth of abutting 

 tissue. This inactive segment may then begin to break down in 

 its external portion, without cutting off a transverse segment 

 beneath to give a "basal cell - ' (figs. 1-4, 5c). Again, a basal 

 segment may be cut off (figs. 56, 6, 11-15), or even two segments 

 may behave in a similar fashion (figs. 8. 9, 10). As the surrounding 

 tissue comes to surpass the original inactive segment, the cells 

 immediately abutting begin to break down in their external por- 

 tions, as did the original segment (figs. 1-15). By continued 

 involving of outer segments the cavity is gradually enlarged, and 

 since the adjacent segments are always more active and therefore 

 have greater turgor, the neck of the structure is narrow, whereas 

 the basal part is broad. 



Meanwhile, more and more of the outer portions of the cells 

 involved break down, becoming mucilaginous and often showing 

 several layers when stained with Lichtgriin (figs. 4, 6, 8, 10, 12, 

 14. 15). Ultimately, all except the portion immediately surround- 

 ing the nucleus having disintegrated, the original segments are left 

 as mere lumps of tissue lining the cavity (figs. 6-15). These basal 

 portions never lose their meristematic activity, but after a period of 

 quiescence begin to put forth papillae as the cavity enlarges (figs. 

 16, 17). These papillae develop into hairs by basipetal segmen- 

 tation, and finally become mature, multicellular, unbranched hairs 

 which fill the cavity and project beyond the opening, out over the 

 surface of the thallus (figs. 15-18). 



Some time after maturity of the hairpit, these hairs are shed, 

 and from the basal portions {of the original segments) new papillae 

 put forth, this time to develop into hairs of a more delicate and 

 fragile nature, often lost very shortly after (figs. 18. 19). Up to 

 this stage there is no appreciable difference between hairpit and 

 conceptacle. Moreover, further development merely offers a 

 means of distinguishing antheridial from oogonial conceptacles, 



