1895. ] On Costaria, 55 
The blade is thin and very brittle, and is covered throughout 
with peculiar reticulations which diminish in size as they 
approach the growing point (the union of blade and stipe). 
The midrib is about twice the thickness of the body of the 
plant, and is broad and smooth, no reticulations ever crossing 
it. The reticulations vary much in prominence; in some in- 
dividuals they are barely visible, while in others they are 
very prominent. The midrib also varies much in plants of 
the same or nearly the same size. In some plants evidently 
mature it is little over 1", while in others of about the same 
size it is often 2" broad. At the base the plant is either 
heart-shaped and abruptly contracted, or in smaller speci- 
mens lanceolate and gradually contracted into a _ short 
thick stipe. From the ends and sides of the stipe innumera- 
ble dichotomously branched rootlets are given off which attach 
the plant very firmly to rocks, etc. Frequently the lower 
half of the stipe is turned abruptly at right angles to the up- 
per half and the rhizoids are then attached to the lower sur- 
HIsTOLOGyY.—A cross section of the stem reveals three 
kinds of tissue; the epidermis, hypodermis and medullary 
layer (fig. 3, ¢, A, and m). The epidermis consists of a single 
tow of cells oblong in cross-section, 16-20/in length, 8 broad, 
the outer wall considerably thickened. In a longitudinal sec- 
tion they are the same shape, showing that they are quadri- 
lateral, the long axis lying in a radial plane (fig. 3, c). 
The hypodermis is made up of five rows of parenchymatous 
cells. The outer hypodermal row is made up of very small 
(8% broad) rounded cells. The remainder of the hypodermis 
is composed of large, irregular, thin walled cells, which in- 
Crease somewhat in size towards the medullary layer (figs. 3, 
and 4,and4). Th plast fined tly tothe outer 
~ or three rows of the hypodermis. 
hea } aa 
ie 
Masia a vVly 4 We 
may distinguish three varieties of cells init: (2) Two or three 
rows of narrow, elongated, rather thick walled cells, along the 
Sides next to the hypodermis (figs. 3 and 5,c). (6) Large oval 
or flask-shaped cells (Schleimgéinge) some of which seem to have 
been formed by the union of two cells. Connected with one 
end of the flask-shaped cells there are long, narrow cells with 
few or no cross partitions. The tubular cell sometimes ends 
blindly and sometimes seems to unite with other cells. he 
