OF SOUTH ■ AUSTRALIA. 
119 
the branches is lost except in the youngest parts. Short, uniseriate, assimila- 
tory filaments, dichotomously branching, may be formed from an initial cell 
a few cells from the apical cell, and these are called triclioblasts, being borne 
in spiral succession and are almost colourless. In some species an early 
abscission of the trichoblasts occurs, but in some they may be retained 
longer. 
Polysiphonia is normally dioecious, the male and female reproductive 
organs being borne on separate plants, but occasionally cystocarpic plants 
may produce spermatangia. The spermatia are borne in a densely 
crowded mass upon short club-shaped branches upon a fertile tricho- 
blast from which they are liberated in large numbers and passively carried 
by water currents to the trichogyne of the female organ, the procarp. The 
procarp develops from a central axial cell next to the apical cell of a short 
lateral ramulus, and this gives rise to a pericentral cell, the supporting 
cell, from which a four-celled carpogonial branch grows outwards and 
upwards in a curved manner so that the terminal cell of the series, which 
will become the carpogonium, is now situated above the pericentral cell from 
which it arose. The terminal carpogonium is at first rounded and uni- 
nucleate, but on mitosis two nuclei are produced, and the carpogonium 
begins to extend forth a process which is to become the trichogyne, and 
one of the nuclei migrates into it to become the trichogyne nucleus and 
the other remains as the female nucleus. Coincident with the extrusion of 
the trichogyne the supporting cell cuts off the two sterile filament initials, 
one basally and the other laterally. The lateral filament initial divides 
immediately, but the basal one remains undivided for a time. 
At this stage fertilization takes place when a spermatium contacts the 
trichogyne, essentially in the same manner as for Nemalion, but in this case 
there is no division of the male nucleus in the trichogyne, and it is a single 
male nucleus which fuses with the carpogonial nucleus. The trichogyne 
nucleus is by now very ill-defined, and the trichogyne withers and dies. By 
now the lateral sterile filament has become four- to ten-celled and the basal 
sterile filament is two cells long. The supporting cell then buds off another 
daughter cell at the upper surface just below the carpogonium, and this is 
the all-important auxiliary cell, which soon establishes a tubular contact 
between the fertilized carpogonium and the supporting cell, so that a muli- 
nucleate fusion cell results containing the diploid zygote nucleus and a 
number of haploid gametophytic nuclei derived from the auxiliary and 
supporting cells. This cell becomes very large, and from the upper portion 
of the auxiliary cell the gonimoblast grows out as a densely compacted 
mass of filaments, each cell of which is uninucleate with a diploid nucleus, 
i.e., the gonimoblast is sporophytic. Elongate carposporangia are borne ter- 
minally at the extremities of the gonimoblast filaments and each contains 
a single carpospore with a diploid nucleus. As the carposporophyte develops 
at first only the auxiliary cell is involved in producing the gonimoblast 
initials, but there is a gradual- fusion of the supporting cells, the auxiliary 
