469 
a primary and two secondary pits, B a transverse wall with four secondary pits. As 
pointed out by WILLE the inner cells of the rib have, a mechanical and a conductive 
function as well. This tissue is covered on both sides by an assimilatory system 
composed of radiating filaments of short cells (fig. 429, comp. WiLLE 1885, fig. 51, 
Kyuin I. c.). 
The lateral veins are opposed, in accordance with their origin from the primary 
cell-rows of the consecutive segments, and run out in the lobes. Lateral veins of the 
Fig. 431. 
Phycodrys rubens. A, marginal part of frond showing formation of secondary pits (#). i interealary division wall. 
450:1. B, group of cells showing secondary pits. In the middlemost cell the inner contour is the outline of the cell 
at high level; the outer contour showing the pits is at a lower level. 380: 1. 
second order may also occur, but they are much feebler. The later arising marginal 
shoots give further rise to lateral veins in the leaves. By treatment with iodine the 
veins take a darker stain owing to their richer contents of starch (July). 
Secondary pits are also produced in great numbers in the monostromatic part 
of the frond; but they arise only at a considerable distance from the top. In the liy- 
ing plant it is impossible to observe their formation, as it takes place only in the 
middlemost part of the walls while the parts of the cells situated at the surfaces 
of the frond do not participate in the process. The formation of the secondary pits 
seems to continue rather long; their number increases downwards and inwards from 
the border. In a leaf examined by me the cells situated near the border (not includ- 
ing the marginal cells) had averagely 2,5 pits, while the cells in some distance from 
the border had averagely 3,6 pits, a difference due to the greater frequency of the 
secondary pits. The secondary pits are recognizable by the transmigrating cell being 
not completely incorporated in the receiving cell but remaining at all events for a 
D. K. D. Vidensk. Selsk. Skr., 7. Række, naturvidensk. og mathem. Afd, VII. 3. 60 
