Uronema elongatum. 
165 
termed U. elongatum. Although its cells in general appearance 
recall somewhat those of a Stigeocloniwn rather than a Ulothrix — 
with which Uronema is most closely allied—yet the alga differs 
from Stigeoclonium in the complete absence of any sign of 
branching, in the method of attachment to the substratum, and 
in the characteristic apical cell. The plants of Stigeoclonium show 
either a differentiation of the shallus into a recumbent basal 
portion, and an erect more or less branched part, or they are 
attached to the subtratum by means of a specially modified basal 
cell aided by rhizoids, as described by Fritsch ; l but in either case 
the method of attachment is different to what obtains in the 
present alga, which recalls rather the basal rhizoidal cell of 
Ulothrix spp, ( e.g ., U. zonata). No species of Stigeoclonium was 
observed in either of the two ponds. 
It has been pointed out by several authors that the genus 
Uronema serves to connect the two families Ulotrichaceae and 
Chaetophoraceae. 2 It may be interpreted on the one hand as a 
stage leading upwards from Ulothrix to Stigeoclonium and its 
allies, or on the other hand as a degenerate and permanently 
unbranched genus derived from the Chaetophoraceae ; or again— 
perhaps the most probable view—as derived from and standing in 
close relation to Ulothrix , but representing a short and blindly- 
ending line of evolution. 3 Extensive cultural work on some species 
of Uronema might help to decide this question. 
Gaidukov 4 found that a form of Ulothrix flaccida Kiitz. 
(=Hormidium flaccidum A.Br.), under certain very abnormal con¬ 
ditions in an impure agar culture, developed more or less apiculate 
end-cells to some of the filaments, recalling somewhat the apical 
cell of Uronema coufervicolum. On the basis of his observations 
he considers that the genus Uronema should be included in 
Ulothrix (sens. ampl.). In this he is supported apparently by 
Oltmanns, 5 and also Wille. 6 However, since the conclusions of 
Gaidukov were based on impure cultures growing under highly 
abnormal conditions, and since U. coufervicolum appears to retain 
its characteristic features—features never yet observed in any 
’ Fritsch, Beih. Hot. Centralb,, 1903, p. 368. 
’ E.g., see Chodat, l.c., p. 267. 
s Compare, e.g., the evolutionary scheme in West’s Algae, Vol. 1, 1916 
p. 282. 
« Uber die Kulturen u.d. Uronnmi-zustand d. Ulothrix flaccida, Ber. Deutsch 
Bot. Ges., 1903, P . 522. 
4 Oltmanns, Morph, d. Algen, I, 1904, p. 203. 
« Wille, Nat. Pflanzenfam. Nachtr. z. Teil 1, Abt. 2, 1909, p. 71. 
