138 



MUSCINEjE 



not strongly defined, partaking of an epidermal character ; the bright red 

 or yellow cell- walls are considerably thicker than those of the central thin- 

 walled large-celled fundamental tissue. In some genera a further differen- 

 tiation takes place of the axial portion of the central cyhnder into a 

 rudimentary ' vascular ' bundle with thicker cell-walls ; similar rudimen- 

 tary bundles being also formed in the pedicel of the sporogone. Both 

 the partially lignified and the thin-walled cells have simple pits in their 

 cell-walls ; these are found in all families of mosses, and are especially 

 abundant in the midrib of the leaves. Some species of Sphagnum (L.) 

 have rudimentary sieve-plates. The central bundle in the stem of Mnium, 

 Polytrichum (L.), and other genera, has been shown by Haberlandt not 

 to possess any of the strengthening functions of a true vascular bundle, but 



Fig. 103. — A^ germinating spore ol Fnnaria kygromeirica L. (X550); s, exospore ; w, rhizoid ; 7', 

 vacuole. B, portion of protoneme ( X 90) ; K. rudiment ot leafy axis ; iu, rhizoid» (After Goebel.) 



to be constructed for the purpose of the conduction of water. Its cells con- 

 tain nothing but a watery fluid, without starch-grains, oil, or protoplasm. 

 In genera which have no such central bundle, like Dicranum (Hedw.) 

 and Leucobryum (Hpe.), the epidermal tissue of the stem and branches, 

 with its perforated cells, forms a similar capillary apparatus. In the 

 more highly developed mosses, Haberlandt notes the following dis- 

 tinct tissues : — (i) an epidermal tissue, sometimes developing trichomic 

 structures ; (2) a mechanical system, consisting of elongated cells with 

 thickened walls ; (3) an absorbing system, most strongly displayed in 

 the rhizoids — also at the base of the sporange ; (4) an assimilating system, 

 often composed of palisade-cells, in the leaves or in the sporange; (5) 

 a conducting system, consisting of the rudimentary ' vascular ' bundles; 



