1891.] Apical Growth of Liverworts. 143 



x" only segments, or whether all are apical cells. Essentially 

 the same thing occurs in Conocephalus conicus, Anthoceros 



Levis, and Riccia. Moreover as stated in a foregoing para- 

 graph, only one apical cell has been found in longitudinal 

 vertical sections, as shown in figures 1, 4, 5, and 6. Yet it 

 may be, from the fact that this row of cells is arranged in a 

 curved position on account of the hinder part being wider than 

 the fore-edge, that longitudinal sections would pass only di- 

 rectly through the long axis of one cell, the others being cut 

 more or less obliquely, thus obliterating the appearance of the 

 segments of the apical cell. ■ In older plants this might per- 

 haps be more probable, but in young plants (and this was the 

 kind used) the planes of the longitudinal axes do not seem to 

 diverge enough to obscure the arrangement of the segments. 



However this may be as to the number of apical cells, such 

 are the facts observed by me, and from these it seems that it 

 is as probable that there is but one as that there are several. 



The resemblance between a fern prothallium and a young 

 thallus of Marchantia polymorpha grown from a spore, js in- 

 ieed very striking, as will be seen upon comparing fig. 7 with 

 a young prothallium. In this (fig. 7) there is but one apical 

 cell whose segments already cut off can be followed without 

 the slightest difficulty. A transverse section through the 

 growing region of a fern prothallium shows a structure similar 

 to that in the liverworts under consideration (fig. 8). Here 

 will be seen one or several initial cells, the number varying 

 with the width of the sinus. 



All sections were cut from specimens imbedded in paraffin, 

 by a Minot microtome. The specimens were fixed in chromic 

 acid 1 pur cent, or absolute alcohol, stained in toto with alum 



cochineal, and countervailed on the slide with Bismarck 

 brown (70 per cent, alcohol solution). The Bismarck brown 

 is a very satisfactory stain for cell walls. 



Indiana University^ Bloomington, Ind., March 5, iSqi. 



Explanation of Plate XIII -Fig. 1, longitudinal vertical section ot grow- 

 ing point of young thallus of Marchantia polymorpha Fig. 2, transverse lon- 

 gitudinal section of similar plant.— Fig 3, transverse longitudinal section 

 through growing point of Asterella hemisphaerica.— Fig. 4, longitudinal vertical 

 section of same plant as &— Fig. % same, of Conocephalus conicus iMg. <>, 

 same, of Anthoceros la-vis.— Fig. 7, young thallus of Marchantia polymorpha 

 grown from spore (after Kny).— Fig. 8, transverse longitudinal section through 

 the apical region of a prothallium of Onoclea struthiopteris; the shaded cell is 

 the egg-cell of an archegonium. . , . .. Al m 



All figures are magnified about 350 diam. except <'» which is about I ,.> aiam. 

 and ; ,,h ut 1'JoOdiam 



