76 b FILICALES. [Acrogens. 



In the early part of 1849, Dr. Wigand published a series of researches on this 

 subject, in which he subjected the assertions of Suniinski to a strict practical 

 criticism; the conclusions he arrived at were altogether opposed to that author's 

 views respecting the supposed formation of the organs, and he never observed the 

 entrance of the spiral filaments into the cavity of the so-called ovule. 



" About the same time M. Thuret published an account of some observations on 

 the antheridia of Ferns. In these he merely confirmed and corrected the statements 

 of NSgeli respecting the antheridia, and did not notice the so-called ovules. 



" Towards the close of the same year, Hofmeister confirmed part of Suminski's 

 statements, and opposed others. He stated that he had observed distinctly the 

 production of the young plant (or rather the terminal bud for the new axis) in the 

 interior of the so-called ' ovule,' but believed the supposed origin of it from the end 

 of the spiral filament to be a delusion. He regards the globular cell at the base of 

 the canal of the ' ovule ' as itself the rudiment of the stem, or embryonal vesicle (the 

 embryo originating from a free cell produced in this), analogous to that produced in 

 the pistillidia of the Mosses. He also describes the development of the ovule 

 differently, saying that the canal and orifice are opened only at a late period by the 

 separation of the contiguous walls of the four rows of cells. 



About the same time appeared an elaborate paper on the same subject by Dr. 

 Hermann Schacht, whose results were almost identical. He found the young 

 terminal bud to be developed in the cavity of one of the so-called 'ovules,' which 

 were developed exactly in the same way as the pistillidia of the Mosses. He stated, 

 also, that the cavity of the ' ovule ' is not open at first, and he declares against the 

 probability of the entrance of a spiral filament into it, never having observed this, 

 much less a conversion of one into an embiyo. 



" In the essay of Dr. Mettenius already referred to, an account of the development 

 of the so-called ovules is given. His observations did not decide whether the canal 

 of the ' ovule,' which he regards as an intercellular space, exists at first, or only 

 subsequently, when it is entirely closed above. Some important points occur in 

 reference to the contents of the canal. 



" The contents of the canal in a mature condition consist of a continuous mass of 

 homogeneous, tough substance, in which fine granules, and here and there large 

 corpuscles are imbedded. It reaches down to the globular cell or ' embryo-sac,' and 

 is in contact with this. This mass either fills the canal, or diminishes in diameter 

 from the blind end of the canal down to the ' embryo-sac ; ' in other cases it possesses 

 the form represented by Suniinski, having a clavate enlargement at the blind end of 

 the canal, and passing into a twisted filament below. In this latter shape, it may 

 frequently be pressed out of isolated ' ovules ' under the microscope, and then a thin 

 transparent membrane-like layer was several times observed on its surface. In other 

 cases the contents consisted of nucleated vesicles, which emerged separately or 

 connected together. 



" The embryo-sac consists of a globular cell containing a nucleus, and this author 

 believes that the commencement of the development of the embryo consists in the 

 division of this into two, which go on dividing to produce the cellular structure of 

 the first frond. 



" With regard to the contents of the canal the author says, ' Although I can give no 

 information on many points, as in regard to the origin of the contents of the canal of 

 the " ovule," yet my observations on the development of the " ovule " do not allow me 

 to consider them, with Suniinski, as spiral filaments in course of solution ; just as 

 little have I been able to convince myself of the existence of the process of impreg- 

 nation described by that author. It rather appears to me that the possibility of the 

 entrance of the spiral filaments and the impregnation cannot exist until the tearing 

 open of the blind end of the canal in the perfectly-formed ovule, as after the opening 

 of the so-called ' canal of the style, in the pistillidia of the Mosses. 



"Another contribution has been furnished by De Mercklin (Beobachtungen an dem 

 Prolhallium der Faivenkrauta; St. Petersburg, 1850), the original of which I have 

 not seen, but depend on analyses of it published in the Botanische Zeitung, and 

 the Flora for 1851, and further in a letter from De Mercklin to M. Schacht, which 

 appeared in the Llnntea at the close of last year. He differs in a few subordinate 

 particulars from M. Schacht in reference to the development and structure of the 

 prothaliium or pro-embryo, and of the antheridia and spiral filaments ; but these do 

 not require especial mention, except in reference to the vesicular end of the spiral 

 filament described by Schacht, which Mercklin regards as a remnant of the parent 

 vesicle, from which the filament had not become quite freed. The observations 

 referring to the so-called ovule and the supposed process of impregnation are very 

 important ; they are as follows : — 



