THE BRYOLOGIST 



Vol. XV May 1912 No. 3 



ABNORMALITY IN MOSS LEAVES 

 H. N. Dixon, M. A., F. L. S. 



Two cases of abnormality in the leaves of mosses, which have come under 

 my notice of late, are described in this note. 



The first is a bifid leaf of Campylopus flexuosus. This has no doubt been 

 produced by an accidental injury to or interference with the growing point of 

 the leaf. That it arose at a very early stage in the development of the leaf is 

 evident from the fact that it is not simply a bifurcation of the nerve after the 

 leaf had developed its normal tissues. In that case there would be no develop- 

 ment of the lamina between the forkings, but only on the exterior sides of the 

 nerve. As a matter of fact the lamina extends down each side of both branches, 

 reaching internally almost to the point of bifurcation. The two halves are 

 approximately equal, so that it appears to be actually a case of forking, not of 

 an outgrowth or branching from the nerve. 



Somewhat similar results have been obtained artificially in the leaves of 

 mosses, e. g. Mnium (cf. V. Schoenau, Zur Verzweigung der Laubmoose; Hed- 

 wigia 51: Heft 191 1). 



The second is, I think, a much more unusual and less easily explained 

 structure. It occurs in a leaf of Tortula muralis, gathered near Northampton, 

 and consists of a transformation of tissue in such a way as to form a structure 

 comparable to a fragmentary adventitious nerve. In the middle of one side of 

 the lamina, a little above the base, a certain number of the normal quadrate- 

 hexagonal and rectangular, parenchymatous cells have been replaced by long 

 narrow, mostly prosenchymatous cells, of a very similar nature to those of 

 which the true nerve is composed, being elongate, of a deep brown color, more 

 or less stereid, and without chlorophyll. Whether they form more than a single 

 layer it is not quite easy to determine (the leaf forms part of a permanent mi- 

 croscopic mount), but in all probability at certain points they constitute at 

 least a double layer. The opposite half of the leaf lamina is quite normal. 



The accompanying figures will give some idea of the structure, fig. c show- 

 ing how at the base of the "adventitious nerve" the abnormal cells pass into 

 the normal parenchymatous tissue. 



I am unable to suggest any cause for the origin of this structure. 



Northampton, England. 



Explanation of Plate I. a. Leaf of Tortula muralis with fragmentary adventitious nerve. 

 b. Portion of the same highly magnified, c. A portion of the same showing how the normal cells 

 pass over into the abnormal, d. Bifid leaf of Campylopus flexuosus^ e. One of the twin apices 

 magnified. 



The March Bryologist was issued March 9, 19 12, 



