296 XXII. REPRODUCTION OF 



separate from one another, so that we can see them separated by 

 a clear interspace (Fig. 109, B). Around the contents of the 

 sporangium is now formed a clear border (E), which soon shows 

 radial striation. This border consists of colourless peripheral 

 protoplasm, the radial structure arises from the numerous small 

 elongated, radially-arranged nuclei, which are here collected (F, G). 

 These nuclei show up clearly only after treatment with suitable 

 reagents, and best after fixing with 1 per cent, osmic acid and 

 staining with alum-carmine. They are only visible with a high 

 power. It can be determined at the same time that from each 

 nucleus arises a pair of cilia. The swarm-spore of Vaucheria is 

 therefore multi nuclear, When the swarm-spore is fully formed, 

 it is at once evacuated. The apex of the sporangium ruptures with 

 a jerk, and at the same moment the anterior part of the swarm- 

 spore issues from the opening, and simultaneously begins to rotate 

 upon its axis. The swarm-spore has to squeeze through the open- 

 ing. Its birth lasts usually somewhat over a minute, a swelling 

 substance formed in the sporangium helping to expel it. In many 

 cases, though comparatively selcfom, the anterior end of the swarm- 

 spore twists off from the hinder part, while still in the sporangium ; 

 the anterior part then hastens to form a complete, but correspond- 

 ingly small, swarm-spore, and the posterior part forms a second 

 swarm-spore. This is only possible by virtue of the multinuclear 

 character of these swarm-spores, in that each half contains the 

 nuclei necessary to its existence. The movement of the swarm- 

 spore lasts about a quarter of an hour ; the direction of the move- 

 ment is not influenced by the direction of the rays of light falling 

 upon it. The swarm- spore is ovate, broader anteriorly ; in this 

 anterior end lies the vacuole. Only in the moment when the 

 swarm-spore comes to rest are the cilia visible; they cover the 

 whole body as a short down. A moment later they are withdrawn 

 into the body of the swarm -spore, which, during this process, 

 shows a wrinkled surface. Afterwards the body again becomes 

 smooth. During the withdrawal of the cilia it is noticeable that 

 the swarm -spore has already surrounded itself with a very delicate 

 membrane. The spore now rounds off slowly ; its colourless 

 border disappears, while the chlorophyll grains come to the sur- 

 face ; the cell-wall rapidly becomes thicker. 



Sexual Reproduction of Vaucheria. In cultures of Vaucheria 

 sessilis, Vauch., sexual organs tend to be produced after some time ; 

 or most Vaucheria may be induced to form them in a few (say six 



