38 
Farmer —On Isoetes lacustris , L. 
ment of the roots and the character of the cambium, and 
secondary thickening. Wahlenberg 1 seems to have been the 
first to notice the peculiar mode of thickening characteristic 
of this plant. His remarks are as follows : ‘ Caudex radicis 
constituitur taleola satis crassa quam nux avellanae saepe 
majore in ceniro vegetante et ad ambitum moritura .’ But with- 
out doubt to Von Mohl belongs the credit of having pointed 
out the fundamental differences existing between the stem of 
Isoetes and those of the other vascular cryptogams which were 
familiar to him. 
Alexander Braun 2 further explained the relation of the 
leaf-arrangement to the conformation of the stem ; and he 
also correctly described the branching of the roots as dicho- 
tomous, although he does not seem to have grasped so clearly 
as Mohl their connection with the stem. 
The chief source of our information on the genus is to be 
found however in the classical memoir of Hofmeister 3 , in 
which the external morphology as well as microscopic struc- 
ture and development, as far as his opportunities admitted, 
are for the most part dealt with in a masterly manner. He 
was, it is true, in error in his statements as to the character of 
the apices of the stem and root, in which he believed he had 
found apical cells ; going so far, in the case of the stem, as to 
correlate the mode of segmentation with the 2- or 3-forking of 
the stem. Naegeli and Leitgeb 4 also came to the conclusion 
that the root-apex was dominated by a 2-sided apical cell, 
although they confess that their view is based on negative 
rather than on positive evidence, and is arrived at after re- 
jecting other apparently possible explanations. Their figures, 
like Hofmeister’s, were wonderfully accurate, and later ob- 
servers have not always paid them the attention which they 
deserve. The results of my own investigations will, I hope, 
1 Wahlenberg, Flora Lapponica, p. 264. 
2 Alex. Braun, Weitere Bemerkungen ueber Isoetes, Flora, 1847. 
3 Hofmeister, Beitr. zur Kenntniss d. Gefasskryptogamen, Abh. Math. Phys. 
Kl. d. Kon. Sachs. Gesell. d. Wissenchaften, 1857. 
4 Naegeli u. Leitgeb, Entstehung u. Wachst. d. Wurzeln, Beitr. zur Wiss. Bot. 
iv. Heft, 1868. 
