CHAPTER XVIII 

 BRYOPHYTES 



WE WILL now study the two great groups of Bryophytes, the 

 Musci or mosses and the Hepaticce or liverworts. They are 

 of little value at the present time except for packing material 

 where it is necessary to retain moisture, but in past ages (the 

 Carboniferous Age) they were much more abundant than at 

 any time since and we are indebted to them for the greater part 

 of our enormous beds of coal which we are now using. 



Mosses. An ordinary moss plant presents an upright stem 

 with three more or less distinct rows of leaves. A more careful 

 examination will show us that this stem is very weak, that it does 

 not contain a fibro-vascular bundle but is composed of elongated 

 parenchyma cells. We will find also that the leaves are com- 

 posed entirely of parenchyma cells and that their apparent mid- 

 rib is composed of elongated cells. These characteristics very 

 readily convince us that we are studying a very simple type of 

 plant as compared with the Pteridophytes and Spermatophytes. 



Arising from the top of this plant is a long, slender stem, 

 ftetea-, bearing a capsuJe which is covered with a cap or calyptra. 

 (Fig. 104, a, ?;.) If we remove this cap we will find the oper- 

 culum (Fig. 104, c), which is a small cover on the end of the 

 capsule. If we remove the operculum (Fig. 104, e) we will find 

 the peristome or teeth (Fig. 104, d.} These teeth are very sensi- 

 tive to varying degrees of moisture which causes them to move 

 inward and outward and thus controls the distribution of the 

 spores which are borne within the capsule. These spores will 

 grow and each produce a filamentous prothallus or protonema 

 which gives rise to new moss plants. 

 164 



