322 



But I am not aware that any one has ever attempted to explain the analogy 

 of its structure until I ventured to introduce the subject very briefly into my 

 Outline of the First Principles of Botany. That perfect unity of design, 

 which is visible in all parts of the vegetable creation, and the constant adher- 

 ence to the construction of every organ of plants, except the stem out of 

 modified leaves, seemed to be deviated from in the Cryptogamic class 

 generally, and in Mosses in particular. An uninitiated person, reading the 

 definition of a genus of Mosses, might suppose that it was in that tribe that 

 the approach to the animal creation, of which so much has been said, 

 takes place. Unacquainted with the exact meaning of the Latin words 

 employed by Bryologists, he might understand by the peristomium a jaw, 

 by the calyptra a nightcap, and by the struma a kind of goitre ; and when 

 he saw that teeth belonged to this jaw, he would naturally conclude 

 that it was really a vegeto-animal of which he was reading. Struck with 

 the evident absurdity of giving such names to parts of plants, without at 

 the same time explaining their real nature, I ventured to call the attention 

 of naturalists to the subject by the following paragraph in the little book 

 above referred to. 



"539. The calyptra may be -understood to be a convolute leaf; the 

 operculum another ; the peristomium one or more whorls of minute flat 

 leaves ; and the theca itself to be the excavated distended apex of the stalk, 

 the cellular substance of which separates in the form of sporules." 



It is now time to shew upon what evidence and reasoning this hypothesis 

 may be sustained. Every one agrees in describing the calyptra as a mem- 

 brane arising from between the leaves and the base of the young theca, and 

 as enveloping the latter, but having no organic connexion with it : when the 

 stalk of the theca lengthens, no corresponding extension of the parts of the 

 calyptra takes place ; so that it must be either ruptured at its apex (as in 

 Jungermannia), or at tlie base ; and in the latter case it would necessarily be 

 carried up upon the tip of the theca, which it originally enveloped. Now, 

 what can be more reasonable than that such an organ, situated as I have 

 described it to be, should be one of the last convolute leaves of the axis 

 which the theca terminates, bearing the same relation to tlie latter as the 

 convolute bractea to the flower of Magnolia, or, to speak more precisely still, 

 as the calyptriform bracteae to the flower of Pileanthus ? If the calyptra be 

 anatomically examined, especially in such genera as Tortula and Dicranum, 

 no dift'erence in its tissue and that of the leaves will be observable ; and that 

 very common tendency to dehisce on one side only as the diameter of the 

 theca increases, which characterises the dimidiate calyptra, may not un- 

 reasonably be understood to be the separation at the line where the margins 

 of the supposed leaf united ; in the mitriform calyptra this separation at a 

 given line does not take place, and the consequence is an irregular laceration 

 of its base. The analogy of the calyptra being of this nature, the next 

 inference would naturally be, that the part it contains is analogous to a 

 flower-bud. Upon this supposition, the external series of parts belonging to 

 this supposed bud would be the operculum ; the adhesion of this to the 

 theca, which would answer to the apex of the axis, or to the tube of the 

 calyx of flowering plants, would be analogous to that which obtains in Euca- 

 lyptus, or perhaps more exactly to that of Eschscholtzia; but it would remain 

 to determine of how many parts, in a state of cohesion, it was made up. In 

 the paragraph above (juotcd, it is stated to be one only ; but I confess I have 

 no better reason to ofl'er for this than the absence of any trace of division 

 upon its surface or in the substance of its tissue, and also perhaps the appa- 

 rent identity of nature between it and the calyptra when both are young, in 

 the Tortula and Dicranum genera already cited. With regard to the peri- 



