324 HOEMEISTER, ON 



cone just mentioned (the first frond). Near it, at the oppo- 

 site end of the embryo, a similar but shorter mass of cel- 

 lular tissue soon begins to protrude (PL XLIII, fig. 15). 

 This is the first root, an adventitious root, differing in no 

 respect from those which afterwards appear in numbers. It 

 grows, like the adventitious roots of the Polypodiaceae and 

 Equisetacese, by division of a cell in the interior of the 

 tissue nearly underneath the apex of the organ. This divi- 

 sion is produced partly by septa almost parallel to the 

 basal surface, which is turned towards the apex of the root, 

 and partly by septa parallel to the lateral surfaces which 

 converge at an obtuse angle. The cells of the second 

 degree which lie towards the apex of the root have the 

 form of a meniscus ; their first division takes place by a 

 vertical septum bisecting the cell, after which a septum is 

 formed cutting the one last formed at right angles. The 

 four cells thus formed divide several times by longitudinal 

 septa, but not by transverse septa (PL XLIV, fig. 2 C ). 

 The part Of the root underneath the punctum vegetationis 

 grows much slower than the part above it. Close above 

 the punctum vegetationis the four outer cellular layers of 

 the root separate from the two axile ones, and an annular 

 air-cavity is produced. A similar air-cavity is formed in 

 the first frond, even in its early youth (PL XLIV, fig. 1). 

 The cells of the prothallium enclose the embryo on all sides 

 even during the development of the first frond and the first 

 root; they are much extended in the direction of the 

 length of this organ, and gradually compressed and ab- 

 sorbed even up to the outermost layer. Contemporane- 

 ously with the first appearance of the root, the part of the 

 embryo w r hich is turned towards the large cavity of the 

 spore, and. separated from the latter by a simple cellular 

 layer, becomes strongly concave (Plate XLIV, fig. I). 

 During the further development of the embryo it becomes 

 more and more arched, until at last it has assumed the form 

 of a short conical cellular mass enclosing an elongated pear- 

 shaped cavity in connexion with the interior of the spore 

 (PL XLIV, fig. 2). The cellular layer of the prothallium 

 which encloses this cavity is afterwards dissolved. The 

 distended portions of the proembryo which enclose the 



