282 
THALLOPHYTES. 
The tissue consists at the surface of small closely-crowded cells ; in the interior it is 
laxer, and the elongated cells are often connected into articulated threads. The cell- walls 
often consist of two clearly distinct layers, an inner thin, firm, compact layer, and an 
outer gelatinous one, capable of swelling greatly in water, which fills up the interstices of 
the cells, and has the appearance of a more or less structureless ' intercellular substance 
it is clearly the cause of the slimy character which the Fucaceae assume after lying for 
. some time in fresh-water. The granular cell-contents have been but little investigated ; 
they appear to be mostly brown, but contain chlorophyll which is concealed by other 
colouring materials; from dead plants cold fresh-water extracts a buff-coloured sub- 
stance ^. The tissue often becomes hollowed out internally into large cavities containing 
air which are forced outwards and serve as swimming bladders. The thallus has not, 
as far as I know, been further minutely examined the outer conformation especially 
has been but little investigated from a morphological point of view. (Gf. Nägeli, Neuere 
Algensysteme.) 
The mode of sexual reproduction is far better known through the labours of Thuret 
and Pringsheim. The antheridia and oogonia are formed in spherical hollows (Con- 
ceptacles) which make their appearance in large numbers and densely crowded at the 
ends of the longer forked branches or of lateral shoots of peculiar form. These con- 
ceptacles are not formed in the interior of the tissue, but are depressions of the sur- 
face which become walled in by the surrounding tissue and so overgrown that at 
length only a narrow channel remains, opening outwards. The layer of cells which 
clothes the hollow is thus a continuation of the external epidermal layer of the thallus ; 
and since the filaments which produce the antheridia and oogonia sprout from it, these 
latter are, morphologically, trichomes. Some species are monoecious, i.e. both kinds 
of sexual organs are developed in the same conceptacle, as in Fucus platy carpus (Fig. 
184); others are dioecious, the conceptacles of one plant containing only oogonia, those 
of another plant only antheridia {e.g. Fucus 'vesiculosus^ serratus, and nodosus, Himantbalia 
lored). A number of hairs which grow in the conceptacles among the sexual organs are 
long, slender, articulated, but unbranched, and project in F, platycarpus out of the mouth 
of the receptacle in the form of tufts (Fig. 184, B). The antheridia are produced as 
lateral ramifications of branched hairs. Each antheridium consists of a thin-walled oval 
cell, the protoplasm of which splits up into numerous small antherozoids ; these are 
pointed at one end, and each is furnished with two motile cilia ; in the interior they 
contain a red spot. The formation of the oogonium begins with the papillose swelling of 
a parietal cell of the conceptacle ; the papilla is separated off by a septum, and divides, 
as it grows in length, into two cells, a lower, the pedicel-cell, and an upper, which 
forms the oogonium ; this swells up into a spherical or ellipsoidal form and becomes 
filled with dark protoplasm. The protoplasm of the oogonium remains undivided in 
some genera {Pycnophycus, Himanthalia, Cystoseira^ Halidrys), and the whole contents 
of the oogonium thus form one oosphere ; in others {Pel'vetid) it divides it into two, four 
{O'zothallia 'vulgaris), or eight {Fucus). Fertilisation takes place outside the concep- 
* In a recent paper (Comptes Rendus de I'Acad, des Sei. Feb. 22, 1869) Millardet showed that 
from quickly-dried and pulverised Fucacese an olive-green extract is obtained by alcohol, which, 
shaken up with double its volume of benzine and then allowed to settle, produces an upper green 
layer of benzine containing the chlorophyll, while the lower alcoholic layer is yellow and contains 
phycoxan thine. Thin sections of the thallus, completely extracted with alcohol, contain also a 
reddish-brown substance which in fresh cells adheres to the chlorophyll-grains, and can be extracted 
by cold water, more easily when the dried Fucus has been previously pulverised. Millardet calls 
this reddish-brown substance phycophoeine. (Compare further the interesting treatise of Rosanoff, 
Observations sur les fonctions et les proprietes des pigments de diverses Algues, in Memoires de la 
Societe des Sei. Nat. de Cherbourg, vol. XIII. 1867 ; and Askenasy, Bot. Zeitg. no. 47, 1869.) [See 
also Sorby, Proc. Roy. Soc. 1873, vol. XXI. pp. 445, 454, 461.] 
2 [See Rostafinski, Beit. z. Kenntniss der Tange, 1876: also Bower, Quart. Journ. Mic. Sei. 
vol. 20, new series.] 
