Dec., 1910.] Self-Dividing Laminae of Certain Kelps. 
2 I 9 
followed; paraffine forming the embedding medium and the sec- 
tions cut 10 mic. thick. The single stain aniline safranin or the 
same in combination with gentian violet were used. The first 
stain gives the middle lamella of gelatinous interlacing food con- 
ducting hyphae a characteristic tint which is of much value in dis- 
tinguishing it from the adjacent cortex. All drawings were made 
with the camera lucida. 
To understand the splitting of the kelp lamina and its relation 
to the tissues through which it passes, a digression must be made 
to set forth the manner of growth in the kelps, with special con- 
sideration of the derivation of the tissues. Three systems of 
tissues make up the kelp thallus: the epidermis, the underlying 
cortex and the central pith-web. Sections of stipe or lamina 
show the hypha-like elements of the pith-web to be highly stretched 
and modified cortex cells and the cortex cells are clearly seen to be 
derived from the epidermal cells, which form therefore the meristem 
in these plants. By periclinal walls the epidermal cells build the 
cortex; by anticlinal ones the epidermal area is enlarged. Hvpo- 
dermal and outer cortical cells are often seen dividing, but the 
total meristcmatic activity of these internal cells is not nearly so 
great as that of the epidermal cells. The cells pushed inward 
from the epidennis reach their maximum size in the middle cortex. 
On the outside of this expanding cortical zone, the epidennis cor- 
respondingly enlarges its area by a constant increase in the number 
of its relatively smaller cells; the division walls of course being 
anticlinal. On the inner side of the expanding cortical zone the 
passive pith-web is seen to consist of much elongated cortical cells 
(trumpet hyphae) between which are large intercellular spaces 
filled with a gelatinous matrix. By this method the large and com- 
plex kelp thallus originates and the various structures peculiar 
to the several genera, including the method of branching under 
discussion, have their origin in variations of this simple process. 
NEREOCYSTIS. 
Nereocystis with its prominent splitting line extending far 
in advance of the cleft, forms an especially favorable type for 
study as portions of the lamina through which the line passed 
could be successively investigated down to the actual fissure and 
the various stages of the process clearly observed. Fig. 2 shows 
a section through the splitting line at a point corresponding to 
Fig. 1, a. The changes from normal lamina are at once seen to be 
a diminution in the thickness of cortex and pith-web, resulting 
externally in the formation of a broad furrow on each side. A 
comparison of the affected region with that of normal lamina at 
either side, discloses the fact that in the middle region the ratio 
of periclinal divisions to anticlinal ones has increased as is evi- 
