422 



SCIENCE 



[Vol. LVI, No. 1450 



MgHPO^. On the seventh day the plants were 

 transferred hack to ICNTO, and the above se- 

 quence continued. The plants were rinsed in 

 distilled water with every change of culture 

 from one solution to another. Whether this 

 apportionment of exposure of culture to the 

 several solutions would continue to he the best 

 for the growth of wheat can not he stated until 

 the plants have matui'ed. It appears the best 

 apportionment of exposure of the plants to 

 the different solutions may vary, being not 

 inconsiderably influenced by the aerial growth 

 environment and by the nutrient requirements 

 of the plant at different stages of growth. 



Because of its simplicity, the method appears 

 well adapted for investigation of these points 

 as well as for instruction in the principles of 

 plant nutrition. It should aid materially in 

 throwing more light on the causative inter- 

 relations of the growth of plants and the com- 

 position of the growth media. 



"W. F. Geeicke 



University of California 



A NOTE ON THE SPERMS OF VALLISNERIA 



After trying for many years to secure favor- 

 able fixation of ovules of Vallisruiria spiralis 

 the writer recently succeeded in getting more 

 fortunate material. Perhaps a few words, by 

 way of preliminary publication, on the method 

 and results may be of interest to workers in 

 this field. 



The ovules are borne numerously in the 

 epigynous ovary surrounded by a mucilaginous 

 substance which greatly retards the action of 

 reagents and is but slowly dissolved by water. 

 Cutting the ovary across permits one to squeeze 

 out the contents which in their mass movement 

 break off the ovules and carry them out. Sev- 

 'eral hours of washing in water are then neces- 

 sary to free these ovules from their gelatinous 

 matrix. In repeated earlier attempts it was 

 found that all ovules having received pollen 

 tubes completed their fertilization and double 

 fertilization before killing agents penetrated to 

 them. If pistils were killed in toto the pollen 

 tubes running down their inner walls in the 

 edge of the gelatin would be well fixed, but the 

 interior ovules were invariably found in poor 

 shape due to the influence of this slime. 



Last year the writer modified the method by 

 lowering the temperature of the water used in 

 dissolving the mucUage from the expressed 

 ovary content. The water was cooled by adding 

 small pieces of ice, and the container was set 

 in a larger vessel of iced water. It was hoped 

 in this way to slow down or stop both growth 

 and cyclosis and to hold aU parts in status quo 

 until killing was possible. 



The results were very satisfactory. Sperms 

 were found not only in the tip of pollen tube 

 within the synergid but in all subsequent situ- 

 ations through to the completion of fertiliza- 

 tion. Many points regarding the male cells of 

 Vallisneria, previously left obscure through 

 poor fixation, were cleared up by use of this 

 material. A brief statement of findings is 

 given below. 



The sperms of Vallisneria spiralis maintain 

 their integrity as male cells until the egg is 

 reached. During the journey through the 

 pollen tube they remain joined end to end and 

 pass out of the tip of the tube together. The 

 sperm that later fuses with the egg emerges 

 from the tube as a cell and immediately flattens 

 against the egg membrane. Many prepara- 

 tions showed the male nucleus with its definite 

 mass of cytoplasm and bordering membrane 

 pressed, as a complete cell, against the egg 

 cyst. One would hardly expect to find, in fixed 

 material, stages showing events at the moment 

 the two cells break together, for the union 

 would probably be completed quickly. But 

 the two masses of cytoplasm must intermingle 

 in some degree in fertilization and probably 

 the male cytoplasm partly or whoUy enters 

 that of the egg. The male nucleus soon moves 

 to the center and unites with the egg nucleus. 

 There can be no doubt of the morphology of 

 the sperm up to the time of its union with the 

 egg, — they come together as complete cells. 



The second sperm loses its cytoplasm soon 

 after it emerges from the pollen tube. Its 

 nucleus is often observed as a spherical body 

 within a strand of protoplasm extending from 

 the egg-apparatus to the polars. Its successive 

 positions suggest thalt it is carried to the 

 polars by movement of cytoplasm within the 

 embryo-sac. The male nuclei of Vallisneria 

 are never vermiform in the slightest degree nor 



