Download PDF

508 University of California Publications in Botany [Vol. 8
Crouar Beems to as to be more properly included in the Ectocarpaceae,
as a further developmenl of such forms as Ectocarpus hemisphericus
and /•:. chantransioides and on the way toward simpler ^giraceae, such
as we conceive may be represented by Microcoryne (cf. Oltmanns, lac.
cit, pp. 25, 26). Sin psit Italia is unknown to us, but on account of its
gelatinous character may possibly be considered to be a slightly
developed, or even degenerate relative of Corynophlaea. Corynophlaea,
if it be distinguished from Leathesia, is more generally solid, with
longer assimilating filaments which are also less swollen at the tip;
Kylin (11)07. p. 83) is of the opinion that the three genera, Micro-
coryne, Corynophlaea, and Leathesia are to be retained as representing
a series in complexity, leading up to the most highly developed species
of Leathesia. As indicated above, Microcoryne, on account of its elon-
gated form and greater or less differentiation of layers seems to
approach Mgvra and the resemblance in structure to Mgira has been
generally noticed and commented upon. Between Leathesia and Cory-
nophlaea there seems to be no satisfactory distinction either as between
solid and hollow, or between longer and shorter cortical filameiits. We
have therefore merged the two genera under Leathesia and designated
the family as Leathesiaceae. We can see no resemblances sufficiently
close to unite Petrospongium with Cylindrocarpus (considering C.
niirroscopicus Crouan as the type). We have therefore kept them
distinct for reasons to be given later.
The Leathesiaceae are carnose algae of flattened or globular form,
solid or hollow, arising from a primitive basal disk, with the inner cells
large and colorless, more or less agglutinated, the cortical cells in
short filaments with chromatophores, without exserted structures of
any kind except colorless hairs, with peripheral growth, and having
gametangia and zoosporangia on the same or on similar plants.
Key to the Genera
1. Zoosporangia more or less difform, usually attached laterally
15. Petrospongium (p. 508)
2. Zoosporangia pyriform to ellipsoidal, attached at the base.. 16. Leathesia (p. 510)
15. Petrospongium Naeg.
Thallus small, thin, flat, usually encrusting rocks, with or without
rhizoids, gelatinous, composed of 3 more or less distinct tissues, viz.
(1) a basal layer, monostromatic ( ?), giving off rhizoids, whence arise
(2) loosely compacted, di- or trichotomous filaments, decumbent below,
curving to erect above, consisting of elongated, cylindrical or swollen.
: