BY G. I. PLAYPAIR. 467 



LEhrenhergii f. minor, one semicell showing distinctly the basal 

 plicse. The pHcse, still more faint, were also noted in a cell of 

 var. Ehrenbergii(P\.x\i., f.5). These plicae are not visible at the 

 edge, over the margin of the cell; and it has been contended that 

 they are of an entirely different nature from the basal granules. 

 On the other hand, I find them occupying the same position on 

 either side of the suture, and replacing the granules in the same 

 cell. Neither granules nor plicae are permanent; as the cell 

 develops the}' are drawn out flat and disappear. Not only so, 

 but the SacM^wm-shape may be observed on a larger scale(Pl.xii., 

 f. 16), with the 6acw^?t?>i-chloroplast, but without either granules 

 or plicse. Finally, a cell has been observed(Pl.xii., f.la) having 

 parietal taeniae proceeding out of an axile chloroplast. Doc. 

 bdcuhcm, therefore, can be looked upon only as a young growing 

 form of var. Ehrenhergii, and a variation of Doc. trabecida. 

 The genus Pleurotcenium also must be included in Docidium. 



»" 



Notes on, and descriptions of various forms. 

 Docidium trabecula Ehr. 



Doc. trabecula Ehr., cf Nag., Gatt. einz. Alg. T.vi., i.Ab. 



Long. semi. 186; lat. bas. 40, centr. 36, ap. 18/j(PI.xi., i.lb): long. 

 . cell. 380; lat. bas. 44, centr. 37, ap. 21/x; Nag. I.e. 



Auburn. 



This is Njigeli's form, the dimensions being in perfect agree- 

 ment. It is a younger form than that generally figured as Doc. 

 trabecula{Fl.x^[., f.9). A still more immature condition(/>. trun- 

 catuni) is shown joined to it(f. la and Pl.xii., f.7). Such forms 

 are quite common here. 



Doc. TRABECULA Ehr., another form(Pl,xi., f.9). 



Long. 300-33.5; lat bas. 35-38; centr.30-33; ap. 20-21//. 



Guildford(78, 114). 



In quantity(114), with var. Delpontel mihi, the intermediate 

 form. This gathering afforded another proof that incrassatioti, 

 scrobiculation, and granulation of the cell-membrane are due to 

 stagnation. It remained for a month corked up in a small phial 



