222 
The Ohio Naturalist. 
[Vol.XI, No. 2, 
The origin of the primary shallow furrows is different from any- 
thing seen in either of the preceding genera. In Lessoniopsis the 
relative increase in anticlinal activity in the epidermis seems to be 
the factor operative in reducing the thickness of the cortical layers. 
The undue stress brought to bear on the cortex by the rapidly 
expanding superficial layer results in the premature transition 
of the inner and middle cortex to the pith-web condition. Ordi- 
narily expansion at the surface in inanimate objects results in 
buckling. In this case the transmission of the stress to the inner 
cortical layers stretches their elements into the thinner or highly 
elongated pith-web condition, thus markedly lowering the upper 
layers so as to produce concavity instead of convexity at the sur- 
face. No figure is given to illustrate this condition as the area 
concerned was far too extensive to be drawn on a scale sufficiently 
large to show the histological changes. 
The second stage or splitting proper is by a process as different 
from that observed in Postelsia as that is different from Nereocys- 
tis. The central part of the mid-rib, after its reduction to the 
thickness of ordinary lamina, is locally still further reduced by 
the action of an internal cortical meristem, associated with a 
quiescent epidermis. On both sides of the medulla in the region 
concerned the cortical cells are seen dividing with anticlinal walls 
(Fig. 12). This has resulted not only in severely attenuating the 
pith-web but on one side the epidermis itself has parted and the 
critical point has been reached, for the thin-walled cells of this 
newly formed tissue cannot withstand the ripping tendencies in 
the wave swayed and twisted lamina. At approximately the same 
stage or on the same slide from which the drawing was made, the 
lamina portions were already separated. 
In healing, the wounds first are covered for a time with a callus 
formation but later the epidermis and cortex heal them over 
exactlv as in Nereocystis. 
MACROCYSTIS. 
The splitting process in this genus was studied by the German 
writers already quoted, but they evidently confined their attention 
to the development of the original perforation and did not study 
the elongation of the cleft, which is carried out by a different pro- 
cess than that forming the perforation. This fact at once sets 
Maerocystis apart from the preceding genera in which the processes 
originating the perforation are also operative in elongating the 
cleft. Sufficient material was available showing the incipient and 
older splits, to make four or five series of sections illustrating each 
of these stages. Part of the material studied came from the 
e ruvian coast, part from Vancouver’s Island. Small and large 
venile laminae, having splits in about the same stage of develop- 
