o. HEILBORN, CYTOLOGICAL STUDIES ON CARICA. 9 



in essential features. The nucleus of the megaspore mother- 

 cell divides, bat no cell-wall and, consequently, no tetrad 

 is formed and the whole mother-cell gives rise to a bi- 

 nucleate embryo-sac (Fig. 7). Both nuclei soon divide, but of 

 the four daughter-nuclei, thus formed, only one (that, prob- 

 ably, a micropylar one!) divides again. Consequently the 

 mature embryo-sac contains but five nuclei, of 

 which three form the eggapparatus (Fig. 8). The other two 

 might be regarded as polar nuclei, though I 

 have never seen any fusion between them, 

 and antipodals are lacking. An embryo-sac 

 of this kind probably represents a reduced 

 Lilium-type. It is, however, not quite clear, 

 if the egg-cell arises from two or from three 

 divisions of the megaspore mother-cell. Hence 

 jthis embryo-sac might as well be characteri- 

 jzed as a modification of the Plumhagella-type 

 [Jcf. Palm 1915). After fertilization, a non- 

 Dellular endosperm (most probably containing 

 diploid nuclei!) is developed and, some- 

 what later, the egg-cell divides and gives rise Fig. 7. Binucie- 



tO the embryo. ate embryo-sac of 



. , . . . , C. chrysopetala; 



Proceeding now to a description of the remains of any 

 reduction division and a discussion of some ^e^i^^d cells can- 



1 n 1 1 • 1 ^°^ °® found. — 



related problems, we shall deal with each spe- Reich. Obj. 7, 

 3ies separately. As the parthenocarpic species °^- -• 



lack male flowers, the reduction division must 

 be sought in their ovules. This is tedious work and in C. 

 zhrysopetala it has not been sucessful. However, in the spe- 

 3ies just mentioned I have seen a binucleate embryo-sac in 

 jrophase, each nucleus showing 9 chromosomes, which is 

 3roof enough that reduction has taken place. Probably the 

 reduction division has been quite normal. Many ovules of 

 ;his species grow to a considerable size without developing 

 iny archesporial cells at all. In many, the embryo-sac de- 

 generates before reaching maturity. Again, many others 

 contain a well-developed embryo-sac, obviously capable of 

 'ertilization. One rather young ovule was found with two 

 irchesporial cells. In larger ovules a very conspicuous pollen- 

 tube is often recognized, a young endosperm having at the 

 »ame time been developed, which shows that cross-fertili/n- 



