( 359 ) 

 EXPLANATION OF PLATES 11 AND III. 



Plate II. Fig. 1 . The figure is an enlargement (about nine-fold) of the original 

 negative. The yellow mercury lines 5701 and 5770 in a non-uniform field. 1 mm. 

 in figure is 0.551 A. U. 



Plate III. Fig. 2 — 5 enlarged 29 times after the original. 



Fig. 2. Middle part of line 5791 in Fig. 1. ( asymmetrical 



Fig. 3. Point of line 5791 in Fig. 1. I separation. 



Fig. 4. Middle part of line 5770 in Fig. 1. ( symmetrical 



Fig 5. Point of line 5770 in Fig. 1. t separation. 



The letters r and v indicate the parts towards the red and towards the violet 

 ends of the spectrum. 



Botany. — "On u double reduction of the number of chromosomes 

 during the formation of the sexual cells and on a subsequent 

 double fertilisation in some species of Polytrichum." By Dr. W. 

 Docters van Leeuwen and Mrs. J. Docteks van Leeüwen- 

 Reynvaan. (Communicated by Prof. F. A. F. C. Went . 



In 1904 there appeared an investigation by Ikeno ') on spermato- 

 genesis in Marchantia polymorpha. Since then quite a number of 

 researches on this subject have been carried out with liverworts. 

 Here and there an occasional reference to the true Alosses lias been 

 made, but, as far as we are aware, nothing has been published 

 on their spermatogenesis since the appearance of Ikeno's paper. 



The older publications, e. g. those of Gdignard '-) and of Stras- 

 burger '), treat exclusively of the final changes of the spermatids to 

 spermatozoids. For this reason we began the present investigation 

 in 1904 soon after the publication of Ikeno's memoir; we obtained 

 results, differing so widely from the ordinary conceptions, that we 

 investigated, not only the spermatogenesis, but also the development 

 and the fertilisation of the ovum. 



The material was fixed at a suitable time, mostly in the field, by 

 a sublimate mixture, and was afterwards stained with iron-haema- 

 toxylin according to Heidenhain. We used Polytrichum piliferum. 

 P. juniperinuni and P. fonnosum. It is our intention to give a 

 more detailed account of the work and of the methods which we 

 have employed, in the Recueil des Travaux Botaniques Neerlandais. 



Ikeno made the remarkable discovery that in the antheridial cells. 

 immediately before division, a small round body passed out of the 



') Ikeno Beihefte zum Botan. Gentralblalt. Bd. 1G, 1903. 

 -) Guignard. Bevue gén. de botanique I. 1889. 

 3 ) Strasburger. Hist. Beitr. Heft IV, 1892. 



