In Aegagropila Sauteri (Ness) Kütz from the very earliest stage there is no differentiation into a cauloid part and a rhizoid part, and the thallus grows in compact spheres or cushions. The lower parts of the thalli (i. e., the oldest segments of the main axis) gradually die, so that the branches are set free from the base upwards. Usually such free thalli are found floating in great quantities in Akan-Lake in Hokkaido. As usually occurrs in vegetative propagation, each separate portion is able to grow into a complete new thallus.
In addition to such vegetative propagation, in summer, asexual reproduction was found in the species brought from Akan-Lake. It takes place by biciliated swarm-spores formed in large numbers, and especially very large numbers are formed in the terminal segment.
Swarm-spores may arise in almost any segment (i. e., apical or median segment) and they escape through an opening which is made by a complete dissolution of the cell-wall at some point near the apex of the segment. In certain cases it was observed that germination of the swarm-spores took place in the segment since there was no opening formed.
Swarm-spores may occur simultaneously in the same filament. The number of swarm-spores vary, for instance, in the apical segment there usually are many swarm spores, but in the median segment they are sometimes fewer in number. In that case, the spores in the apical segment are smaller than those in the median segment.
The asexual swarm-spores are pear-shaped and possess two cilia of equal length. The spores are therefore motile and are of an intense green color, and are completely filled with cytoplasm, one nucleus, a visible red eye spot, a few bowl-shaped chloroplasts and food-reserves. The spores are positively phototropic, their apical end being towards the source of light.
It is evident that the swarm-spores germinate only after a period of rest, and each produces a new filament directly.
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