( 82(; ) 



the spore mollier-eell undergoes, iiiid wiiicli will l)e disciussed below. 

 We may however at once pohit out, that in the formation of embryo- 

 sac and egg-cell, the whole apparatus remains in the same place, 

 and is therefore never surrounded by the iuner integument. 



The portion of the nucellus lying below this, is now elongated 

 by the extreme stretching of a single cell (or in some cases perhaps 

 two cell^) in the central and in each of the 5, 6 or 7 peripheral 

 rows of cells, of which it consists. The nuclei often also assume an 

 extended shape, so that one gets the inii)ression that a passive 

 stretching has taken place. At the same time a digestion of the longi- 

 tudinal walls occurs, and tinally the [)rotoplasts also coalesce more 

 or less. In this way a great cavity arises, contaiuing j)rotoi)lasin, 

 often in a })eriplieral layer and with 6, 7 oi- 8 nuclei, perhaps 

 sometimes even more in consequence of nuclear fragmentation, which 

 seems to occur. 



If an ovule is examined in this stage, without the history of its 

 development having been traced, this cavity is inevitably regarded 

 as the embi'yo-sac, and the real embryo-sac, which lies above it, is 

 then taken for the egg-api)aratus. It is in this way that Warming, 

 who, for want of the necessary material could only trace part of 

 the development of the ovule, has regarded things.^) This pseudo- 

 embr>^o-sac remains in existence during the further development of 

 the ovule to the seed, and is only compressed more o;' less in some 

 cases by the large increase in size of the cells of the inner integu- 

 ment, which has already been dealt with above. When the embryo 

 begins to develop it grows out into this pseudo embryo-sac, in the 

 same way as would happen with a true embryo-sac. 



We may now pass on to consider the fate of the spore mother- 

 cell. At a certain j^eriod its nucleus shows a clear synapsis stage. 

 In the division, which follows this, the reduction of the number of 

 chromosomes therefore probably takes place. The tixation was not 

 sufficient to allow one to conclude with certainty that a hetero-typic 

 division of the nucleus occurs (the nuclei are moreover extremely 

 minute) ; such observations as were made, leave very little doubt, 

 however, when considered in connection with the preceding synapsis, 

 that the luij)loid generation begins here. This nuclear division is 

 followed by a cell division and the formation of a dividing wall. The 

 upper of the two cells, which ai'e thus formed, gradually degenerates 

 and becomes more and more flattened by compression ; remnants of it 



1) EuG. Warming. Familien Podostemaceae. II. Afhandling. Kgl. Danske Vidensk. 

 Selsk. Skr. 6le llaekkc, nalurv. og math. Al'd. 2det Bd. III. Kjobenhavn, 1882. 

 Compare eg. p. 05 (107). 



