Farmer.— On Isoetes lacustris , L. 39 
show the source of their misconception of the structure of the 
apex. 
The structure and development of the Stem . — As far as the 
structure of the stem is concerned, however, it is much more 
difficult to understand on what grounds it was possible for so 
careful an investigator as Hofmeister to describe its growth as 
regulated by an apical cell. At no time is any cell-arrange- 
ment perceptible which would warrant this conclusion, and if 
the appearance presented by sections cut parallel to the furrow 
of the stem occasionally seems to point to it, more careful 
study of a series invariably leads to an opposite result, and 
clearly shows that the mistake is referable either to the ob- 
liquity of the section or to the fact of its having passed 
through the base of a leaf-rudiment. Comparison of trans- 
verse with longitudinal sections fully confirms this observation 
(PL V. Figs. 11, 13), and further affords proof that the apical 
meristem is even less regular than is the case in the Lycopo- 
diaceae, judging at least from the figures published by Stras- 
burger 1 and others. The entire apex of the stem is covered 
by a columnar layer of cells which divide chiefly anticlinally, 
periclinal divisions only occurring at rare intervals, a fact 
which is to be connected with the slight increase in length 
of the stem. I endeavoured to find out if the frequency of 
the periclinal divisions bore any relation to the number of 
leaves formed, but have been unable to ascertain that any 
such connection exists. The cells which lie beneath the su- 
perficial layer, though irregular in size and shape, indicate, in 
their general arrangement, a conformity with Sachs’ law. 
Hegelmaier 2 and Bruchmann 3 have regarded the bundle of 
the stem as consisting partly of a sympodium of leaf-traces, 
and partly of a cauline portion, represented by xylem-elements 
derived from a supposed plerorne-tissue which surmounts the 
woody portion of the bundle. A comparison of a great 
1 Strasburger, Coniferen u. Gnetaceen, Taf. xxv. figs. 29, 30. 
2 Hegelmaier, Zur Kenntniss einiger Lycopodinen, Bot. Zeit. 1874. 
• 3 Bruchmann, Ueber Anlage u. Wachst. d. Wurz. bei Lycopodium u. Isoetes , 
Jen. Zeitsch. fur Naturwissenschaften, VIII. 
