278 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



connection with the experiments, showing beyond a doubt that the 

 female plants treated were absolutely sterile. 



Loeb has shown that, when unfertilized eggs of the sea-urchin are 

 placed for one and one-half to two minutes in a mixture of 50 c.c. of 

 sea-water+3 c.c. of 0. 1 m acetic, butyric, or other fatty acid and then 

 transferred to normal sea- water, a fertilization membrane is formed. 

 This method was applied to unfertilized Fucus eggs. In experimenting 

 with the eggs those used at any one time were always divided into three 

 lots. One lot was used as a control, another was fertilized, and the 

 third was treated with the solution. If a single egg in the control 

 formed a cell-wall, which seldom happened, the three lots were dis- 

 carded. In case the eggs were treated with acetic or butyric acid, 

 as above described, a large number of them formed in about ten 

 minutes a membrane or cell-wall which was exactly similar to the one 

 formed about normally fertilized eggs. By plasmolyzing the eggs the 

 membrane is readily seen. Eggs not treated with a solution or not 

 fertilized undergo cytolysis and degenerate. In any case many of the 

 eggs failed to develop, but about one-fourth as many formed mem- 

 branes under the influence of the solutions as were formed about ferti- 

 lized eggs. After the formation of the membranes if the eggs are 

 placed in hypertonic sea-water, 8 c.c. to 10 c.c. of 2.5 m NaCl or KC1 

 +50 c.c. sea-water, for 30 minutes and are then brought back into 

 normal sea- water, development continues. Nearly all of the eggs 

 which have formed a membrane become pear-shaped, showing a 

 rhizoidal papilla, and by next morning have cleaved. The rhizoidal 

 cell is cut off and one or more cleavages have taken place in the other 

 portion of the sporeling. If the cultures are properly aerated, spore- 

 lings develop resembling in every respect those grown from fertilized 

 eggs. In place of sea-water containing a fatty acid, solutions of 

 various other cytolytic substances were used, but none stimulated 

 membrane formation or development as well as the acids. 



With regard to the first formation of the cell-wall over the surface 

 of isolated masses of plant protoplasm, it is usually attributed to a 

 process of secretion by the outer layer. That the process is a rapid 

 one is shown by the fact that in Fucus eggs a cell-wall is formed in ten 

 minutes after the entrance of the sperm. Cell-wall formation may also 

 be artificially induced, as shown above, by various substances. In 

 some cases a cell-wall may appear under certain conditions on the sur- 

 face of plasmolyzed protoplasts in fifteen minutes, as has been shown 

 by Klebs, Palla, and others, while in other cases hours are required 



