( 270 ) 



three nuclei of the egg-apparatus and (lie polar nucleus are formed 



so that division nevertheless takes place three times. 



In Oen. Lain. I never found a nucleus or remains of a nucleus 

 in the lower part of the embryosac, whilst the four nuclei always 

 lie in the upper portion. A few times it was possible to observe 

 the divisions themselves. Thus I found an embryosac, in which 

 the nucleus was dividing into two, with its spindle in the long axis 

 of the embryosac. Further I found embryosacs with two nuclei, 

 which were sometimes superposed, sometimes side by side. Therefore 

 the lower nucleus probably changes its place, coming to lie higher 

 up in the embryosac. The divisions of these two cells were also 

 found, namely two spindles, in the upper part of the embryosac, 

 and at right angles to each other. In the same manner the spindles 

 are found in most plants above and below in the embryosac, at 

 the third division in couples perpendicular to each other. The division 

 of these two nuclei in Oen. Lam. is therefore pretty certainly the 

 last division of the embryosac, in which the two synergids are 

 formed from one nucleus, and the egg-nucleus and the upper polar 

 nucleus from the other, hi this particular embryosac, with the two 

 spindles at right angles to each other, there was moreover no trace 

 of nuclei at the chalazal end. We may therefore assume, that in 

 Oen. Lam. the first division in the embryosac is suppressed, so 

 that antipodal cells and lower polar nucleus are not formed at all, 

 and that there is not even an antipodal initial cell, which occasionally 

 degenerates again after being formed, as in Heloals and Mourera. 



In the embryo-sac of Cypripedium the number of the divisions is 

 still further reduced; here, according to Miss L. Pack 1 ) there occurs 

 in the embryosac only one homoiotypic division in the lower cell; 

 the upper cell degenerates. The homoiotypic division is not followed 

 by- a cell-division. The two nuclei in the lower cell now arrange 

 themselves at the poles; this cell grows out longitudinally and the 

 nuclei divide again, so that they are four in number. Further 

 divisions do not take place in the embryosac; the four nuclei 

 become egg cell, synergids and upper polar nucleus. 



When in Oen. Lam. the four nuclei have been formed the syner- 

 gids, which lie nearest to the micropyle, surround themselves, like 

 the egg-nucleus, with their own plasma; the upper polar nucleus 

 remains free in the plasma of the embryosac. 



The four cells, which have arisen in the pollen mother-cells through 

 the reduction division, grow out regularly to pollen-grains; the 

 method of origin and the structure of the walls probably agrees in 



l ) Lula Pace. Fertilization in CypripL'ilium. Uotanicalliazeüe. XL1V. 1907 p. 353. 



