METHODS 17 



the sides converging somewhat in front. In vertical longitudinal section 

 it appears also triangular, but very much broader (Fig. 8, D). A cross - 

 section (Fig. 8, A, B) shows that the lateral faces meet above and below 

 at an acute angle, so that the whole cell has somewhat the form of a 

 triangular wedge, with the edges directed respectively dorsally and ven- 

 trally. The segments cut off from the lateral faces are large, and ordinar- 

 ily are formed alternately right and left. Before a dichotomy occurs, how- 

 ever, more than one segment may be cut off successively on one side, and 

 one of these presumably gives rise to the apical cell of the new branch, the 

 branching being in the strict sense of the word not a true dichotomy. 



In horizontal and vertical longitudinal sections the arrangement of 

 the segments derived from the apical cell is much the same. In cross- 

 section the elongated, almost oval cell appears surrounded by the crescent- 

 shaped segments (Fig. 8, A, B). Fig. 8, A shows a cross-section of the 

 thallus apex shortly after the dichotomy is complete, and the growing 

 point of the new branch is established. The lobes a, a', are the beginnings 

 of young antheridial scales, while the group of cells, b, is the growing 

 point of the new branch. The divisions of the apical cell are not in quite 

 the same plane as those of the original apex. 



Each segment cut off from the apical cell first divides transversely 

 into an adaxial and an abaxial cell. The latter cell divides only by walls 

 perpendicular to the plane of the thallus, and contributes to the wing or 

 lamina of the thallus, which remains permanently but a single cell in 

 thickness. The adaxial cell divides crosswise into a middle and an inner 

 cell. The former forms the outer tissues of the midrib, and also from 

 it arise the antheridia. The innermost cell, by subsequent repeated lon- 

 gitudinal divisions, gives rise to the narrow cells of the conducting strand 

 traversing the midrib. These cells at first have dense contents, which 

 later mostly disappear. A section of the young conducting strand is 

 shown in Fig. 7, B. 



The entire apex of the shoot, and the younger antheridia, are bathed 

 in mucilage which is secreted by two-celled glandular hairs developed 

 from the outer cells of the young segments ; and similar mucilage secret- 

 ing hairs are also found among the antheridia. 



Pallavicinia Levied Schiffner 



Pallavicinia Levieri, the third species considered here, is much less 



restricted in its distribution. It is quite common in the neighborhood of 



Tjibodas in Java, at an elevation of 1400-1 500 metres, and material was 



collected at several points. It has been reported from several other sta- 



