SPECIAL MORPHOLOGY : MOSSES. 183 



136 



constitute the processes, and those of the latter the cilia, as, for instance, 

 in Hypnum, and Bryum. A perfect, closed cell never, however, concurs in 

 forming the folded membrane, nor the processes and cilia (so far as they 

 are free from the interior outward). A wider field for more compre- 

 hensive and exact observations is opened here than I have hitherto been 

 enabled to pursue. 



I must not omit to mention a view which was first proposed by the 

 acute Robert Brown *, namely, that in most peristomoses* the regular 

 number of the teeth was 32, and that when fewer were present it must 

 be considered owing to a growing together of several into one. At first 

 sight this view presents much in its favour. But the circumstance that 

 this law is not applicable to Mosses, the peristomium of which exhibits 

 a greater number of teeth, is at once suspicious ; besides, the history of 

 development of the capsule of the Moss shows, as far as our knowledge 

 of the subject extends, that we cannot speak of growing together in 

 this case, but merely of more or less regular splitting down. Finally, 

 regularity of number in teeth is by no means so firmly established as 

 many might assume, for we not unfrequently find peristomse in which 

 there is one tooth too little, especially in the Mosses where the number 

 of the dentations exceeds 32. The almost regular divisibility of the 

 number of teeth by four must, however, always strike us as remarkable. 

 The reason of this appears to be based upon the nature of the vegetable 

 cell, and is thus determined with reference to teeth from their first forma- 

 tion. A comparison of the multiplication of cells in some of the Algce, 

 as, for instance, in Meyen's Tetraspora, with the almost constant forma- 

 tion of four spores and pollen-granules in one parent cell, together with 



* Robert Brown's Miscellaneous Writings. (Germ. Trans. II. 734.) 



186 Hypnum alrietinum. Cross-section of the still green sporocarp, in the region where 

 the cilia and processes are connected at the base. , A deposit of thickened cells form- 

 ing the operculum ; b, separate cells, forming the dentation of the exterior peristomia ; 

 c, thickened walls, formed by a row of cells constituting the cilia and processes ; the 

 latter consist of parts which project externally, in the form of a Gothic arch. 



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