No. 1I.] THE BRYOPHYTES OF CONNECTICUT. 13 
sometimes so closely that it cannot be separated without injury. 
It develops two types of rhizoids, both of which represent 
simple outgrowths from cells. In one type the walls are thin 
throughout; in the other they bear scattered local thickenings 
in the form of short rods which project into the lumen. The 
rhizoids are all short-lived, and those of the first type simply 
anchor the plant to the substratum; those of the second type, 
however, by means of capillarity, play a certain part in the 
process of absorption. In addition to the rhizoids, the thallus 
often bears longitudinal rows of delicate scales,on the lower 
surface. These are developed very early and arch up over the 
growing point, thus protecting it from injury. 
The thallus is more or less differentiated, and always shows, 
at least in certain stages of development, a distinct epidermis, 
beneath which the photosynthetic tissue is situated. The latter 
consists of green cells loosely arranged with intercellular spaces 
containing air among them. In the higher forms these cells 
are in distinct air-chambers, which communicate with the out- 
side air by means of pores in the epidermis. In the lower 
forms they simply line the intercellular spaces, and the com- 
munication with the outside air is often less definite. The 
Marchantiales are divided into two families, the Ricciaceze and 
the Marchantiacee, which differ from each other most 
markedly in the structure of the sporophyte. 
The Ricciacez include both aquatic and terrestrial species, 
and are usually smaller than the Marchantiacee. The ter- 
restrial forms grow in old fields, along damp roadsides, and 
on the muddy borders of ponds. The thallus, which rarely 
attains a length of fifteen millimeters, forks repeatedly in 
one plane, thus giving rise to a characteristic rosette. All the 
New England species are annual, developing their sporophytes 
in the autumn. The aquatic Ricciacee are larger than the 
others, and rarely produce sporophytes, the tips of the thallus 
being able to survive the winter. When they become ter- 
restrial, they sometimes assume an appearance very different 
from their normal aquatic state. 
The archegonia in the Ricciacez are so deeply immersed 
in the thallus that only their necks protrude above the surface. 
In consequence of this fact the sporophytes begin their 
development beneath the surface, and they retain this position 
