118 MR. HENFREY ON THE DEVELOPMENT 



stage of the progress. The extreme delicacy of the young prothallium renders dissection 

 a matter of some difficulty, and, as in the embryotomy of flowering plants, the anatomist, 

 with all the skill acquired by practice, must be content to obtain decisive observations in 

 but a very small proportion of his preparations. 



The drawings which accompany this Memoir were nearly all made by means of the 

 camera lucida eye-piece, so that they represent preparations actually seen ; the unimport- 

 ant details alone, such as the green colouring matters, &c, being given in a conventional 

 manner, except in a few separate figures devoted to the special illustration of these 

 points. 



The first part of the Memoir is devoted to an account of my own observations ; to this 

 is added a critical examination of those of preceding authors ; and, in conclusion, a few 

 remarks on the general bearing of the results upon vegetable physiology. 



As some foreign vegetable anatomists have been inclined to lay great weight on the 

 quality of their microscopes, in discussing the points in dispute between different observers, 

 it may be as well to state, that my investigations were made with one of Ross's large 

 microscopes, with his 1-inch, ^-inch, ^-inch and ^-inch objectives (about seven or eight 

 years old), and the drawings sketched in with the camera lucida eye-piece, after the pre- 

 parations had been fully observed with various other eye-pieces. The ^-inch objective 

 sufficed for most purposes ; the ^-inch was useful for the spermatozoids, but in regard to 

 anatomical points was chiefly used on account of the short focus, which is often advan- 

 tageous where the lines of cell- walls cross above one another. The most important point, 

 however, is the clearness of the preparations observed, and on these I place my depend- 

 ence as to the accuracy of my statements, since there can be no doubt of my microscope 

 being quite equal to those of foreign investigators. 



I. The Prothallium. 



The specimens which I investigated were obtained from the Chelsea and Regent's Park 

 Botanic Gardens, consisting in a great measure of self-sown plants collected from the pots 

 of ferns growing in the stoves. Hence I am unable to give a very definite statement as 

 to the species of ferns on which I made my observations, and can only say that they were 

 chiefly species of Gymnogramma, Adiantwm, Tteris and Asplenium ; this is of the less 

 consequence, since the phenomena appeared to differ very little in the different specimens 

 in which specific distinctions were certainly known to exist. 



Plants of Gymnogramma chrysophylla and of an unknown fern were obtained in the 

 earliest condition, for among the tufts of young prothallia placed beneath the simple mi- 

 croscope for separation, I often found the burst capsule of the parent plant, with the 

 spores germinating within and growing out from it. Examination of these showed that 

 the first change which occurs in the spores is the bursting of the outer tough coat and the 

 protrusion of the delicate inner membrane as a kind of pouch, like a pollen- tube from the 

 pollen-grain; this tubular process grows longer, and sooner or later becomes divided by I 

 cross partition into two cells (figs. 1 & 2) ; this is sometimes formed near the spore ; 

 other cases the first cell is produced into a long filament before the cross-wall is forme 

 and the latter then partitions off a small portion at the end. The second cell become 



