180 Atkinson . — A Monograph of the 
Some very fine specimens have been found in such situations. 
On the other hand, no streams seem to be too large, provided 
there are places where currents of water pass forcibly against 
the surface of rocks. It is generally stated that they inhabit 
the water of cold mountain streams, but any of our streams 
distant from the mountains furnish excellent examples where 
the other conditions obtain. 
The members of the subgenus Sacheria seem, in general, to 
require water more thoroughly agitated, while the members of 
the subgenus Lemanea will, in some cases, flourish where there 
is little agitation, provided a deep and fairly strong current 
bathes some obstruction in an otherwise quiet stream. In 
this respect there is, naturally, some variation in species. 
The plants are generally attached to rocks, but are some- 
times attached to woodwork in the streams. 
The plants are usually collected during the summer months, 
when, in many cases, the specific characters are not discern- 
ible. Collections should be made at several periods during 
the year, generally in late autumn, midwinter, early spring 
and summer. Even then latitude and temperature of stream 
must be consulted, in connection with some specific peculiari- 
ties of the plants themselves, to yield really valuable specimens 
to the collector. 
II. Morphology of the Plant-parts. 
The carpospore produces the Le7nanea-p\d.nt by a rather 
complex, indirect, mode of development 1 . In an annual 
cycle of the polymorphic oophyte there are three distinct 
successional forms. It will be well at the outset to state 
briefly these forms and characterize them. 
i. Prostrate form 2 . The first of these is the prostrate 
(permanent) form. It lives from year to year, not only re- 
producing itself, but in the autumn developing the earliest 
1 It is not to be inferred that these forms represent a perfect ‘ alternation of 
generations.’ 
2 Sirodot, Ann. d. Sci. Nat., loc. cit., ‘tissu proembryoniforme ; ’ Bornemann, 
loc. cit., ‘ Haftgevvebe ; ’ Wartmann, loc. cit., * niederliegende Strahlen.’ 
