118 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



4 megaspore nuclei undergo only one division to give rise to the 8 

 nuclei of the mature embryo sac. They no doubt observed certain 

 peculiarities and curious appearances which could not be explained 

 on this interpretation, but these were disregarded as abnormal or 

 even "pathological" conditions. 



Bambacioni (1928a, 6) showed that in Fritillaria and Lilium the 

 formation of the 4 megaspore nuclei is not followed directly by the 

 8-nucleate stage but by a secondary I^-nucleate stage, in which the 

 2 chalazal nuclei are much larger than the micropylar. This comes 

 about in a very peculiar manner. At first there is a 1+3 arrange- 

 ment of the megaspore nuclei (Fig. 76A-D) so that the 3 chalazal 

 nuclei come to lie very close to each other. During the next stage 

 the micropylar nucleus divides normally, but the three chalazal 

 spindles fuse to form a single common spindle (Fig. 7QE-F), so 

 that at the close of the division there are two haploid nuclei at the 

 micropylar end and two triploid nuclei at the chalazal (Fig. 76 

 G-H). One more division occurs, resulting in 8 nuclei, of which 

 the 4 chalazal nuclei are triploid and the 4 micropylar are haploid 

 (Fig. 767). The mature embryo sac thus consists of three haploid 

 cells (the egg and two synergids), three triploid cells (the antip- 

 odals), and a tetraploid secondary nucleus formed by the fusion of 

 the two polar nuclei, one haploid and the other triploid (Fig. 76/). 

 Of the antipodals, the two lowest frequently show a flattened and 

 degenerated appearance — a condition originating from the fact that 

 the basal nucleus of the secondary 4-nucleate stage often divides in 

 a more or less abortive fashion. 



Cooper (1935a) extended the observations of Bambacioni to sev- 

 eral other species of Lilium, and since then the Fritillaria type has 

 been demonstrated in a general way for the entire tribe Lilioideae and 

 several other genera belonging to diverse families; Piper, Heekeria, 

 Myricaria, Tamarix, Cornus (some spp.), Armeria, Statiee (most 

 spp.), Rudbeckia (most spp.), GaiUardia, Cardiocrinum, Gagea, 

 Erythronium (most spp.), Tulipa (some spp.), and Clintonia (see 

 Maheshwari, 19466, for detailed information). 



It may be noted that the fusion of the 3 chalazal megaspore 

 nuclei may take place when they are either in the prophase stage 

 or in early metaphase. In the former case the secondary 4-nu- 

 cleate stage is preceded by a secondary 2-nucleate one, and the 



