﻿ON THE DEVELOPMENT OF THE STEM AND LEAVES 

 OF PHYSIOTIUM GIG ANTE UM Weber. 



By Jesse Beeves. 

 (Plate 339.) 



The genus Physiotium includes some of the most interesting 

 forms of liverworts, owing to the presence of auricles or water- 

 holding sacs ; these occur in a more or less complicated form in 

 nine out of the ten species, the exception being P. (Anotium) para- 

 <h>.non Jack, and reach a high state of complexity in P. giganteum. 

 Fig. 1 represents a small shoot seen from the dorsal aspect, and 

 fig. 2 part of another shoot seen from the ventral aspect. The 

 shoots bend outward from the tree to which they are attached, and 

 grow vertically upward. 



An examination of the stem disclosed another remarkable 

 iz„ that it grows by a 2-sided apical cell, instead of the 

 3-sided cell hitherto supposed to be of universal occurrence in the 

 acrogynous Jungermannieee. Fig. 3 is a transverse section through 

 the top of the apical cell, which takes the form of a 2 -sided wedge 

 with sharp edges ; the side, however, is not formed by a simple 

 curve, as is usual in this type of cell, but by two open curves which 

 meet at the centre to form an obtuse angle. Segment (1) is still 

 undivided; segment (2) is divided into two equal halves; while 

 segment (3) has again undergone division in its lower (ventral) 

 half. Fig. 4 is a section from the same apex taken a little lower 

 than the preceding, and it is here readily seen that the second 

 cuts off the cell which goes to form the auricle, while its 

 sister cell adds to the upper lobe. In view of this, it is possible that 

 the auricle represents an amphigastrium, and the apparent upper 

 lobe the fused upper and lower lobes. These latter will, however, 

 be together referred to as the upper lobe throughout this paper. 



The mature auricle in various species of Physiotium has already 

 been described and figured by Jack.* In P. giganteum it is a 

 slightly bent subulate sac (fig. 5). The circular mouth, bounded 

 by a strong collar, opens on the side next to the stem ; it is closed 

 within by a curtain from which hang the two dissimilar flaps of the 

 valve (fig. 6). One of these flaps is exactly like the rest of the 

 auricle in texture; the other, the clapper, consists of squarish, 

 thin-walled, empty cells, which are evidently dead. At the junction 

 of the latter with the curtain the cells are elongated transversely, 

 and the walls are thinner ; and to this is no doubt due the easy 

 movement of the clapper whereby the opening and closing of the 

 valve is effected. The auricle is attached to the upper lobe of the 

 leaf from the lower side of the mouth to its base (fig. 7). 



An interesting provision for the conduction of water into the 

 cavity of the auricle may be here described. The upper lobe is well 



* "Monogr. d. Lebermoosgattung Fhysiotium," Hec 

 Journal of Botany.— Vol. 32. [Feb. 1894.] 



