—31— 



had disappeared, the plants themselves were mostly overturned by the winter's 

 alternate freezings and thawings, and had I not known the exact spot, I would 

 have had great difficulty in finding the moss. The following summer the banks 

 unfortunately fell in, and in consequence our rarity disappeared. — G. N. Best. 



THE PERISTOHE— I. 



By a. J. Grout. 



The peristome, besides being one of the most beautiful of microscopic ob- 

 jects, is also one of the parts most carefully considered in classifying mosses. 

 The details of the differences in development and structure of the various types 

 of peristomes have never been presented in English in a popular form. M. 

 Philibert in the Revue Bryologique has given a masterly presentation of the sub- 

 ject, but it is in French, and too e.xtended and technical to be of popular inter- 

 est. 



This series of articles will be based largely on the work of Schimper and 

 Philibert, but will in no sense be a translation of either. Free use will be made 

 of Schimper" s illustrations published in his various works, and these will be sup- 

 plemented by original drawings. 



The simplest type of peristome is 

 that of Georgia ( Tetraphis), where the 

 tissue which fills the operculum splits 

 into four equal parts, as is shown in 

 the accompanying figure. The oper- 

 culum is composed of a single layer of 

 cells, and is easily deciduous. 



It is an interesting fact that in An- 

 dreaea and Georgia, which have a 

 thalloid protonema indicating a close 

 relationship to the hepatics, the capsule 

 divides into four parts. In Andreaea 

 the whole capsule dehisces as in the 

 hepatics; in Georgia, only that portion 

 of the tissue lying within the opercu- 

 lum. Prof. D. H. Campbell in his 



Structure and Development of the 

 Mosses and Ferns, states that he con- 



siders this resemblance an accident. I am not so sure that this is the case. If 

 he be right, the division of these capsules into four parts, and the division of all 

 moss peristomes into multiples of four, may possibly be explained by the regu- 

 larity of the divisions of the two-sided apical cell from which the sporophyte is 

 developed. It will readily be seen that in Georgia no spores are found within 

 the operculum. This is true of mosses having any other type of peristome. In 

 all other types, the central tissue forms the columella, which in most cases 

 shrinks up into a small piece of tissue upon the falling of the operculum. 



