185 



ON THE DEVELOPMENT OF THE THECA, AND ON THE 

 SEXES OF MOSSES. 



(Continued from page 169.) 



" The outer peristome,'" observes Mr. Valentine, " is universally considered to 

 arise from the theca itself ; whilst the inner is believed to arise from the internal 

 membrane, or columellar membrane of this paper. The necessity of substituting 

 this name will presently appear. To say that the outer peristome arises from the 

 theca would give an incorrect idea both of its origin and connexion. It is 

 continuous at the base, with a delicate lining membrane, which is very intimately 

 attached to the theca. The existence of this lining membrane, which has hitherto 

 escaped the notice of observers, may be proved by taking a portion of the theca 

 from which the columellar membrane has been detached, and carefully separating 

 the peristome from above downwards, when the lining membrane will remain 

 attached to the base. A very thin longitudinal section will also show the division 

 of the theca itself into an external and internal layer. The former, when mature, 

 is of a dense coriaceous or even horny texture ; whilst the latter is of a loose 

 spongy cellular tissue. The most favourable examples to prove this fact by 

 dissection are found in the genus Tortula ; but the Hypnums, a genus very remote 

 from Tortula, are by no means unfavourable. The term lining or internal mem- 

 brane ought properly to be applied to this newly-described layer ; but to prevent 

 confusion, it appears desirable to abandon the use of this name altogether, and to 

 supply its place with the term columellar membrane, designating the proper lining 

 of the theca the thecal membrane. The inner peristome is continuous with the 

 columellar membrane, at the point where this last is attached to the inside of the 

 stoma. These peristomes are not always found. Some genera are altogether 

 destitute of them, while others have only one, which, as far as my observations 

 have gone, is always the external." 



After naming several instances in illustration of these several facts, Mr. 

 Valentine proceeds to describe the development of the sporules, which process 

 he supposes may commence at the time of the separation of the columellar 

 membrane from the columella. After alluding to the opinions of Dr. Hooker, 

 Dr. Brown, Dr. Greville, and Mr. Arnott, Mr. Valentine says, " My observations 

 have convinced me that the sporules are formed from a gummy fluid, which is 

 secreted either by the columella or columellar membrane (most probably by both), 

 and that this secretion becomes cellular by the gradual separation of the fluid 

 from the solid part ; the separation taking place in numberless points throughout 

 the whole mass of secretion. As the little particles of fluid increase in size, the 

 solid material increases in density, until it has assumed the consistence of mem- 

 brane, which forms an envelope for every separate particle of fluid. Each of these 

 particles, with its investing membrane, then detaches itself from its neighbour 



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