— 145 — 



more carefully, and at the same time a report on the embryo- 

 formation in certain other Hieracium-specles will be given. 



Murbeck in the aforesaid paper has promised to describe 

 more carefully the development of the embryosac in Hieracium, 

 but as the species, which are described in the present paper, belong 

 to another group and besides are experimentally treated by 

 Ostenfeld, 1 consider that a statement on my investigations of 

 even just this material has its justification together with Murbeck's 

 work on this subject. 



In the following investigation it is perhaps suitable to begin 

 with a description of each form and thus first turn our attention 

 to H. auricula, which, like //. venosum, 1 have found to be quite 

 normal. The castrating experiments in this case provided negative 

 results (Ostenfeld 16, p. 233). 



I. Hieracium auricula. 



The material originates from a spontaneous plant from Jutland, 

 now growing in the Botanical Gardens of Copenhagen. 



In very small heads, about 3 mm. broad, one first observes 

 indications of the division of the nucleus in the pollenmothercells. 

 I have already had opportunity of pointing out the great advantage 

 afforded by the Compositae for a cytological examination of the 

 development of the germ-cells: one has often in the same section 

 through the head a great quantity of various stages. In the head 

 of a Hieracium, however, there is not such a great difference in 

 the grade of development of the different flowers as for instance 

 in Calendula, Tanacetum (Rosenberg 23) and others. 



Another advantage is, that the anthers are very long, so that 

 even in the same sporangium the PMC are in different stages of 

 development, the lower part being generally a little earlier in deve- 

 lopment than the upper portion. 



Figur 1, PL I, shows a nucleus in a PMC in a very early 

 stage, at the close of the resting period with the first indications 

 of nuclear-division. It is just about the same stage which Allen 

 (1) names „the period of the nuclear reticulum". The nucleus- 

 contents consist of an uniformly distributed, but very ragged and 

 irregular reticulum. Here and there at different points the chro- 

 matic material is found collected together at the periphery of the 

 nucleus, and there are generally two nucleoles. 



