igif,] ROE— CONCEPT ACLE IX FUCUS 237 



organs, the other nothing but paraphyses, is an interesting point, 

 but does not bear on the phylogenetic history of the conceptacles 

 themselves." She then proposes the term "vegetative concep- 

 tacle" as meaning ''those cavities in the thallus which have been 

 developed only in a vegetative direction." In commenting on 

 Barton's theory, Murray (18) says (p. 60) "I know so little 

 about the ancestors of the Fucaceae, that I must be content with 

 a respectiful attitude toward this statement." 



In their research upon Splacknidium, Mitchell and Whitting 

 in 1892 (17) find that the conceptacle is developed by alteration 

 of one of the epidermal cells, close to the apical cell, which becomes 

 peculiarly modified but is inconsequential; however, they consider 

 it the homologue of Bower's initial, although it takes no further 

 part in developing the conceptacle, the real work falling to the 

 neighboring cells. 



In interesting connection with work on the conceptacle is that 

 on hairtufts and sori in groups outside the Fucales. 



Mitchell in 1893, in a study of Hydroclathrus (16), finds groups 

 of hairs analagous to " Fasergriibchen " (cryptostomata) of the 

 Fucaceae. In development they certainly resemble the con- 

 ceptacles, and her description recalls Reinke's work. She speaks 

 of an isolated cell or group of cells which become separated from 

 surrounding epidermal tissue. Transverse division results in 

 formation of hairs from these isolated cells. Meanwhile growth of 

 the thallus leaves the isolated portion in a slight depression. Later, 

 the sporangia which are developed in close proximity around the 

 hairpits mature, and after liberation of the spores the sporangial 

 walls disappear and the basal cells originate new growth. Finally, 

 all the sporangia disappear and these hairtufts. with central depres- 

 sions, are left scattered over the thallus, persisting throughout the 

 life of the plant. Mitchell concludes that although not a true 

 conceptacle, such as in the Fucaceae, yet the growth of both hairs 

 and reproductive organs is initiated by alteration in form and sub- 

 sequent division of epidermal cells which might with truth be 

 called "initial" cells. "My observations do not exclude the possi- 

 bilitv of the initiative being taken by a small group of initial cells 

 dividing simultaneously, instead of a single one." 



