482 Mr. Valentine on the Development of the Theca, 



sporae, but, from their very small size, he could not obtain a positive convic- 

 tion of the fact. According to my own observations, these " mother cells" 

 are the true sporse, and the bodies which he considers the sporae are the gra- 

 nular contents, arranged in three or four distinct masses, as I have before 

 described. Dr. Mohl also advocates the propriety of considering the internal 

 membrane as belonging rather to the columella than as forming a lining 

 membrane to the theca, which coincides with the view I have offered of its 

 nature. 



EXPLANATION OF TAB. XXIII. 



Fig. 1. A very young "pistillum"of Orthotrichum anomalum before the burst- 

 ing open of the tubular style at the apex. The solitary cell is seen 

 at the bottom of the canal. 



Fig. 2. A " pistillum" more advanced ; the base having begun to enlarge, the 

 apex of the style open, and the second cell formed. 



Fig. 3. The pair of cells from the last fig. dissected out. 



Figg. 4. & 5. Cells dissected out from more advanced "pistilla." 



Fig. 6. Another very young "pistillum" of Orthotrichum Li/ellii, showing 

 more clearly than fig. 1 . the tube passing down to the cell. 



Fig. 7. Two primary cells of Tortula ruralis dissected out, and one of which 

 is burst open to show the moving particles. 



Fig. 8. A section of the tubular style of Orthotrichum affine. 



Fig. 9. The pistillum of Orthotrichum Lyellii, a little before the separation 

 of the upper part to form the calyptra. The style is decayed. 

 The longitudinal folds are nearly peculiar to the species. 



Fig. 10. A section of the last. The young seta is in the centre, showing a 

 division or arrangement of the tissue into the axis and cortical 

 layer. The wall of the pistillum has separated from the seta and 

 become plicated. That the pistillum does not enlarge at the base 

 by distention (from the growth of the supposed germen within) is 

 evident, as there is a considerable space between the two. 



