Acrochaetium catenulatum M.Howe

Ocm 1
Acrochaetium catenulatum sp. nov.
Epiphytic, minute, mostly 50-150 n high; the single basal cell
(spore) subglobose, 8-1 in in diameter; the single main axis
suberect or ascending, 9-11 p. in diameter, usually 10-20 cells long,
commonly arcuate and with a secuiul series of mostly simple and
often successively shorter branches along the convex side, the
branches beginning with the basal cell or often several cells higher,
now and then irregularly alternate or very rarely opposite, ulti-
mate ramuli 7-8 ¡i in diameter; cells mostly as long as bread,
often a little less long than broad, rarely twice as long, usually
quadrate-orbicular in optical section, now and then discoid and
occasionally biconcave or concavo-convex, the cell wall rather
thick and gelat inous especially in basal and median parts, mostly
1-2 n thick; chromatophore (?) apparently occupying nearly the
whole cell except for a few small irregularly disposed vacuoles;
hairs apparently wanting; monosporangia 9-11 n long, 5.5-7.0
wide, thinner-walled than the vegetative cells, finally terminating
the main axis and most of the branches and commonly also, sessile
and secund along the outer (convex) face of the arcuate-hamate
upper half of the main axis, the emptied sporangia sometimes
refilled by the subjacent cells, two (rarely three) successive ter-
minal cells of axis or branch often converted into sporangia
.simultaneously. [Plate 31, figures 12-18.]
On Chaetomorpha cartilaginea in beach drift, La Punta, region
;of Callao, January 25, 1907, Coker 38 p.p., associated with Acro-
chaetium clandestinum, Goniotrichum Cornu-cervi, G. Alsidii,
Pl-eonosporium venustissimum, Erythrotrichia polvmorpha, Ecto-
carpus sp., etc. The short often flattened-globoid or even occa-
sionally discoid cells, combined with the rather thick gelatinous
walls, give young unbranched plants (see figure 14) some super-
ficial resemblance to young conditions of Goniotrichum Alsidii,
with which they are sometimes associated, but the filaments of the
Acrochaetium have a less diameter and thp:	^re thinner,
The cell contents are very homogeneous aiu	-latter
Acrochaetium
85
appears in our formalin-preserved material to be generally dif-
fused, except for minute vacuoles, while in the accompanying
Acrochaetium clandestinum the chromatophores have more or les-,
definite forms as described and figured under that species. We
find no trace of a pyrenoid in the vegetative cells, but in the spores
there is a denser central body that sometimes shows a starch
reaction with iodine.
Plate 31, figures 12-18. Acrochaetium calenulaltim
12.	A single plant, showing mode of branching, form of the cells and chromatophores,
one emptied and three filled monosporangia, etc.
13.	A portion of another plant, showing three two-celled lateral branches in each r,f
which the terminal cell becomes a monosporangium and in two <>l which
the other cell al60 becomes a monosporangium simultaneously.
14.	A young unbranched plant with a terminal monosporangium.
15.	16. Plants with short secund branches and hamate-arcuate axes. The mono-
sporangia are here secund and sessile or terminate the short branches.
17.	A plant with alternate, opposite, and irregular branching.
18.	A plant with secund branches, of which the lower are longer than the main axis
(here shown in a horizontal position).
All figures from plants on Chaetomorpha (La Punta, region of Callao, Coker 38
p.p.). Figures	3 are enlarged 675 diameters; 14-18, 390 diameters.
12 18 \CKOCHAKTJUM CATENULATUM M, A. Howe
NEW YORK BOTANICAL GARDEN
02141479
02141479