233 



who embrace Ihe opposite view, like 04 u i g n a r d and 

 B n n i e r, will think the use of thèse terms admissible. 

 Altliough we incline towards this latter opinion, we shall 

 not dwell on this point hère. 



But we think it désirable to point out that a doser 

 study of unfertilised ovules, especially of dioecious plants 

 will perhaps yield surprising results. Since we know through 

 L o e b that chemical stimuli may cause the development 

 of an egg, the possibility must be granted that this may 

 also be the case with higher plants. When a normal fer- 

 tilisation does not take place, such chemical stimuli would 

 at any rate render a beginning of development possible. 

 Looked at from this point of view the case of Dasylirion 

 is perhaps important, but, as we stated already at the 

 beginning of this communication, only an investigation 

 in the natural place of occurrence of the plant can give 

 an answer to this and allied questions. 



EXPLANATIOX OF THE FIGURES IN PLATE V. 



Ail the figures represent ovules or parts of ovules from 

 Dasylirion acrotrichum ; the dates are given, on which the 

 material was gathered. 



Fig. 1. X 100. Top of an ovule with 2 integuments, micro- 

 pyle, top of the nucellus and embryosac 

 (22'id August). 

 „ 2. X 240. Top of an ovule; only the inner integu- 

 ment is sketched. In the top of the em- 

 bryosac two cells are seen, which perhaps 

 belong to an egg-apparatus; in the next- 



