208 HOFMEISTER, ON 



Development of the vegetative organs. — The similarity in 

 the development of the different species of ferns does not 

 extend beyond the formation of the rudiments of the first 

 frond and of the first root. 



So far as regards the mode of development of the vege- 

 tative organs, the two commonest ferns of Germany re- 

 present the terminal points of the long series of multi- 

 farious forms of the most extensive family of the vascular 

 cryptogams. Pteris aquilina affords one of the most per- 

 fect examples of a fern with a creeping stem, having the 

 fronds arranged in tAvo lines, and with a most decided 

 tendency to bifurcation of the terminal bud. The greater 

 number of the ferns inhabiting the forests of the torrid 

 zone comport themselves like Pteris aquilina. Aspidium 

 flix-mas, on the other hand, forms a stem tending up- 

 wards, and agrees essentially in its habit, in the arrange- 

 ment of its fronds, and in the division of its vascular 

 bundles, with the tree-ferns of the tropics. The follow- 

 ing observations will treat of the history of the develop- 

 ment of the two ferns just mentioned, and we will pro- 

 ceed first with Pteris aquilina. 



Pteris Aquilina, L. — The surfaces of the septa formed in 

 the cell of the first degree in the first frond of Pteris aquilina 

 are turned towards the apex of the stem.* A plane passing- 

 through the longitudinal axis of the stem and of the frond, 

 is at right angles to the lateral surfaces of the wedge-shaped 

 apical cells of both organs (PI. XYIII, fig. 6). Even at a 

 very early period, before the enveloping cellular layers of 

 the prothallium are ruptured by the longitudinal growth of 

 the first frond, septa are formed in the apical cell of the 

 frond on the right and left of its median line. These septa 

 are at right angles to the fore and hind walls, and they change 

 the form of the cell, which has hitherto been wedge-shaped 

 like a segment of an ellipsoid, into a three-sided prism with 

 the edge turned downwards and having its hinder surface 



* This is the case also with all the subsequent fronds not only of Pteris 

 aquilina but also of other species of the same genus ; as well as with the fronds 

 of such ferns as Pteris serrulafa, which have a ^triple frond -arrangement, and 

 where the apical cell of the terminal bud has the form of a three-sided inverted 

 pyramid. In the Polypodiums and Aspidiums the circumstances are widely 

 different. 



