THE HIGHER CRYPTOGAMIA. 187 



all essential points. The only specific differences are, that 

 in certain species (such as Aspidium filix-mas, and several 

 species of Adiantum) certain marginal cells of the pro- 

 thallium grow into papillae, which in Aspidium are thin and 

 cylindrical with a clavate end, and in Adiantum are very large 

 and flask-shaped, whilst in the prothallia of other ferns the 

 margin is destitute of such protuberances, as is the case 

 in Pteris aquilina and serrulata. The only known instance 

 of variation is afforded by Ceratopteris thalictroides. When 

 the large spores of this species germinate, and the exospo- 

 rium bursts, it is seen that the portion of the prothallium 

 which is enclosed within the lobes of the exosporium, is a 

 multicellular roundish body. The conclusion from this fact 

 is that the inner cell of the spore is divided into several 

 daughter-cells before the bursting of the exosporium. The 

 prothallium moreover does not develope two lateral lobes 

 with a deep indentation between them, having the focus of 

 continuous cell-multiplication, at its base, but the point of 

 most active cell-multiplication is situated sideways on the 

 prothallium (PL XXIV, fig. 16). One wing only of its 

 fore edge is developed. The rudimentary cells of the 

 antheridia are for the most part marginal cells of the pro- 

 thallium somewhat deeply buried between the vegetative 

 cells of the margin. The process of cell- division in them 

 coincides with that which is supposed to exist in most of 

 the Polypodiaceas (PL XXIV, figs. 1719).* 



* Wigand states that the mother-cells of spermatozoa, and even motile 

 spermatozoa themselves, are sometimes found in the chlorophyll-bearing vege- 

 tative cells of the prothallium. This statement has not been confirmed by any 

 other observer. Wigand has probably seeu appearances which I have myself 

 met with, though on rare occasions. I have found in mauy of the vegetative 

 cells of old, abnormally developed, prothallia, globular or elongated, sharply 

 defined masses of a thick mucilaginous substance which for the most part hung 

 together in arborescent ramifications, but were to some extent detached, and 

 formed entirely free globular bodies. The diameter of these bodies is but little 

 (about a third) greater than that of the mother-cells of the spermatozoa. They 

 wei;e present in individual cells sometimes in greater sometimes in less num- 

 bers. The arrangement of the "chlorophyll of the cells in which they were 

 enclosed was not materially disturbed although the colour of the chlorophyll 

 was slightly faded. Some of the arborescent groups were drawn out at one 

 end into a thin thread-like cell which had quite the appearance of a fungoid 

 filament, and which was attached at its extremity to the free outer wall of the 

 cell of the prothallium. In other cells of the same prothallium the chlorophyll 

 had disappeared and they were filled with empty cells having a firm membrane 

 and looking like the mother-cells of zoospores. These structures are certainly 



