—79— 



did not agree with Lorentz that the less developed side of the duplicate leaf 

 (vaginant lamina) of Fissidens is the side which is always in the shade. He 

 thought that the inequality of the leaf parts may be due to the relative position 

 of the leaves in the bud. This conclusion is accepted by Pettier from his studies 

 on various mosses. 



The mosses studied by Pottier were fixed in Kaiser's fluid, dehydrated, 

 cleared, and embedded in parafhn. The stained serial sections, mounted in 

 balsam, served as a basis for study. Reconstructions of certain leaves in plastiline 

 or modeling wax were also made from the outlines of cross-sections. 



Studies of the Andreaeales 



The initial cell of Andreaea crassinervia Bruch has a single face, but the 

 initial cell of A. angustata Lindb., with a single face, may be replaced by an initial 

 with two faces. Leaves that have an initial cell with two faces develop a large 

 broad leaf without a midrib; those leaves that have an initial cell of one face 

 usually form a normal acicular leaf with a midrib. The above facts added to the 

 observations of previous investigators indicate that these archaic plants show a 

 tendency toward the type of leaf development found in more recent mosses. 

 [Campbell, D. H. Mosses and Ferns p. 182, 1913, describes the two forms of 

 apical growth of Andreaea leaves.] In all the species of mosses studied, Pottier 

 considered asymmetry the result of pressure of one leaf upon another while in 

 the bud. The side of the leaf which is covered reaches a less advanced stage of 

 development. 



Studies of the Bryales 



The most important feature in the study of the leaf of Mnium undulatum 

 and M. punctatum is the "development of the midrib. For the first species, 

 Pottier presents a diagram indicating a leaf cross-section with eight primordial 

 cells arranged in one row. Upon comparing the figures of the actual cross 

 sections of M. undulatum leaves figured, in no case is there a section with 8 

 primordial cells arranged in a single row. The author's theory of development 

 for the midrib of M. undulatum is entirely at variance with the actual cross- 

 sections of this moss. The method of development of the midrib as explained 

 for M. punctatum will serve equally as well for the first species described. Here 

 two initial cells take part in the formation of the midrib. Each of the initial 

 cells divide by a wall parallel to the surface of the leaf so that in cross section 

 the midrib now shows a group of four cells. The two dorsal cells are divided by 

 a periclinal wall into an outer and an inner cell. From the inner cells by further 

 division is formed the group of small conducting cells, tracheids or stenocysts, 

 that traverse the center of the midrib. The two ventral cells from the group of 

 four cells resulting from the division of the initials, also divide by a periclinal 

 wall into an inner and an outer cell. From the two inner cells by further division 

 is formed a group of large much thickened cells, eurycysts, which serve for 

 strengthening the leaf. 



The development of the leaf in Funaria hygrometrica is comparable to that 



