THE GENUS POLYSIPHONIA. 281 
The nucleus of the carpogonium divides to form two nuclei, one of which 
becomes the female gamete nucleus ; the other enters the trichogyne, which 
becomes elongated and constricted where it joins the carpogonium. 
When a spermatium becomes attached to the tip of the trichogyne, the 
walls between dissolve and the contents of the sperm enter. The sperm 
nucleus, which contains 20 chromosomes, passes into the carpogonium ; the 
male and the female nuclei lie in close proximity, while the trichogyne 
nucleus disintegrates and the trichogyne shrivels. The nuclei in the carpo- 
gonium fuse, and a set of auxiliary celis are developed by the pericentral cell 
round the fertilized carpogonium. With the fusion of the two nuclei the 
number of chromosomes is brought up to 40, and the sporophyte generation 
has begun. The carpogonium then fuses with the auxiliary cell, which lies 
between it and the pericentral cell, A fusion with the pericentral cell itself 
follows immediately, and the fused sexual nucleus, which has divided into 
two, moves down to the pericentral cell. After this, the passage between the 
carpogonium and the auxiliary cell closes, and the earpogonium remains 
isolated, finally breaking. down with the three sister-cells of the carpogonial 
branch. During the formation of the auxiliary cells from the pericentral 
cell, each nucleus in the first three cells of the earpogonial branch divides, 
the daughter-nuclei lying side by side in pairs. The protoplasmic connection 
which exists between the auxiliary and pericentral cells becomes larger, and 
the nuclei of the auxiliary cells move towards the pericentral cell. This 
veneral union results in the formation of a large cell, which was called by 
Phillips (46. p. 289) the * central cell.” lt contains many nuclei, two of 
which are sporophytic, the others gametophytic. The sporophytie nuclei 
divide and the central cell develops lobes, into each of which a sporophytic 
nucleus passes. The nuclei again divide, and a carpospore is cut off ter- 
minally, the lower part remaining as a stalk cell, attaching the carpospore to 
the central cell. After the formation of the carpospores, the central cell 
increases in size greatly, absorbing the stalk cells. The envelope of the 
eystocarp is developed from the peripheral siphons of the original procarpic 
branch, and is lined with delicate filaments, the paranemata, which arise from 
the cell of the axial siphon. Tue eystocarp is urn-shaped, with an ostiole at 
the top, through which the carpospores are discharged. 
SuMMARY. 
Species of British Polysiphonia may be classified according to their 
anatomical differentiation. The thallus consists of a central siphon, sur- 
rounded by four or more pericentral siphons. In the corticate forms, 
external cells are also present which do not extend for the complete length 
of an articulation. Protoplasmic continuity is present throughout the plant 
in the young stages, although later some of the connecting pits may become 
closed, 
