STRUCTURE.] SPORES ANALOGOUS TO POLLEN. Ill 



caused by the separation (not dissolution) of the tissue, 

 gradually enlarging, form the cells of the anther, in which 

 the viscid secretion takes place. This secretion is afterwards 

 converted into pollen, in a manner similar to that in which 

 the sporules are formed. When the anther is nearly ripe, a 

 still further separation of the tissue takes place, and the four 

 cells become two. When perfectly mature, these cells dehisce 

 longitudinally at the lateral furrows. In Buxbaumia the 

 theca frequently dehisces longitudinally after the manner of 

 some anthers; whilst in Solanum the anther dehisces by a 

 pore at the apex, thus approaching the ordinary dehiscence 

 of the theca. The lining of the cells, or Endothecium of 

 Purkinje, may be considered analogous to the columellar 

 membrane." (Linn. Trans., vol. xvii.) 



Mrr Valentine afterwards supported these views by new 

 observations, and at considerable length. I can only quote 

 a part of the evidence on which he believes that the truth 

 of his opinion is established. 



"The analogy," he observes, "which exists between sporules 

 and pollen is so remarkable, and the particulars so numerous, 

 that the essential identity of the two can, as I conceive, be 

 scarcely a matter of opinion. In the first place, the sporules 

 are formed in thecse, which have a great resemblance to some 

 anthers. They are in most instances surrounded by a. peri- 

 chsetium, which is a collection of modified leaves analogous 

 to the perianth. They are either sessile, or seated on a stalk 

 or seta, which may be named the filament. In Sphagnum 

 the theca is elevated on a pedicel or leafless prolongation of 

 the axis, of which peculiarity the anther of Euphorbia is a 

 parallel instance. The thecse are one-celled, yet they have a 

 columella, which may be likened to the connectivum ; and, 

 although the connectivum usually divides the anther into two 

 cells, Callitriche is an instance in which there is but one 

 cell ; and there are examples in which the cavity is spuriously 

 divided into four cells, as in Tetratheca, which, in this re- 

 spect, resembles the theca of Polytrichum ; and in the fact of 

 evacuating its contents by a single pore, resembles the 

 general structure of thecae. All thecse are lined by a distinct 

 membrane, and so nearly does this resemble the endothecium 



