PLATE XVm.— RED SEA- WEED (Polysiphonia Subulata)— continued. 



Fig. 1. Male Plant 



Antheridia, or male sexual organs, are cone-like, supported by a short stalk. 

 Forked hair on the outside of each, protecting it 



Fig. la. Ripe Antheridium in optical section ( x 430). 



There is a basal-cell forming the Stalk, a row of cells in the centre forming an Axis, and the mother-cells of 

 the Anthefozoids : are grouped around this Axis. The Antherozoids are spherical motionless masses of protoplasm, 

 discharged into the surrounding water by the bursting of the ripe mother-cell. 



Figs. 2 and 3. Female Plant 



Carpogonia, or female sexual organs, are obovate, when ready for fertilisation, and consist of three principal 

 parts — 



1. Foot or attachment 



2. Fertile spore-forming part This is the swollen portion, and consists of a central cell surrounded by 



a number of peripheral cells. 



3. Hair apparatus, consisting of the forked hair and the Trichogyne (Gr. trichos, hair ; gone, seed). 



Fig. 4. The process of Fertilisation is extremely interesting, beqause of the part that Infusoria have recently been found to play 

 in it The antherozoids, discharged into the surrounding sea-water by the bursting of the ripe antheridia, are passively 

 floated about by the waves, since they are motionless in themselves, and they may accidentally come into contact with 

 the trichogyne of a female plant ; but their chances are greatly increased by the action of unconscious agents, such as 

 Infusoria, which create currents in the water in the neighbourhood of the female organs. 



Vorticella, or the Bell Animalcule, is a stalked Infusorian, attached to this red sea-weed. The stalk may either 

 be lengthened out, as in the drawing, or shortened by being coiled into a spiral. The bell is surmounted by a 

 crown of cilia which move in a definite order, so as to cause currents which will sweep particles of food down the 

 gullet The Vorticella is at first a free-swimming unstalked bell, but with the stalk it becomes fixed, and it 

 naturally settles down where there is likely to be an abundance of food. The currents set up necessarily send 

 antherozoids down the gullet, but some come in contact with the apex of the trichogyne, and are retained there. 

 The forked hair, too, will serve to break the force of the current, and form a sort of eddy, so that the antherozoids 

 may the more readily settle down where wanted. The antherozoid thus blends with the trichogyne, and its sub- 

 stance passes down the canal of the trichogyne, till it reaches the central cell, and thus fertilisation is effected. 

 The forked hair and trichogyne both disappear after fertilisation, having served their purpose. 



Life History. — The Red Sea-weeds multiply by a simple non-sexual process, or are reproduced sexually in a somewhat complicated 

 manner. 



The contents of certain cells break up into four portions, which escape by rupturing the cell-wall, and germinating 

 reproduce the parent plant These are the Tetragonidia produced non-sexually. 



In some red sea-weeds the male and female organs are on different parts of the same plant, but in Polysiphonia they 

 are on different plants. The Male plant produces Antheridia, which begin as a single-celled branch, then become a row of 

 cells, and finally a cone-like mass of cells. The forked hair arises from the stalk-cell, and the other cells produce the 

 rounded Antherozoids. The Female plant produces Oogonia, but as they become spore-fruits after fertilisation, they are called 

 Carpogonia. These arise, like the Antheridia, from a single cell, which eventually becomes a basal portion or Foot, con- 

 sisting of a ring of four cells, and one in the centre ; a middle or Fertile portion, consisting of a large central cell, sur- 

 rounded by a number of cells; and a top portion, consisting of a long cell or Trichogyne, with a forked hair. An 

 Antherozoid reaching the apex of the trichogyne, in the way already described, is retained there, and strange to say, the 

 fertilising effect is produced at some distance in the central cell and surrounding cells of the Carpogonium. The surrounding 

 cells grow and divide till they form a fruit-like cover, while the central cell forms a number of close-set branches, at the ends 

 of which the Carpospores are developed. There is thus a Spore-fruit formed, which discharges its so-called Carpospores or 

 Endogonidia by a hole at the top; these on germination give rise to young plants. 



