122 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



the Fritillaria type, the only difference being that in Plumbagella 

 the development is arrested at the secondary 4-nucleate stage and 

 the fourth division is omitted. 



Adoxa Type. The Adoxa type, formerly known as "Lilium type," 

 is characterized by all 4 megaspore nuclei undergoing just one more 

 division to form an 8-nucleate embryo sac having a normal egg 

 apparatus, three antipodal cells, and two polar nuclei (Fig. 78). 

 It was described for the first time by Jonsson (1879-1880) in Adoxa 

 moschatellina and later by Lagerberg (1909) and Fagerlind (1938a). 



Until only a few years ago there was a long list of plants under 

 the Adoxa type. With the publication of Bambacioni's work and 

 the consequent reinvestigation of Lilium, Fritillaria, and several 

 other genera, its ranks have steadily diminished and there are now 

 only five genera in which its occurrence is a more or less regular 

 feature: Adoxa, Sambucus, and some species of Erythronium 10 , 

 Tulipa, and Ulmus. 



An interesting variation has been reported in some species of 

 Tulipa. In T. sylvestris (Bambacioni-Mezzetti, 1931) vacuolation 

 frequently commences even at the megaspore mother cell stage, 

 and all the 4 megaspore nuclei gather at the micropylar end of the 

 cell, where they divide to give rise to a group of six cells (one of 

 which is to be interpreted as the egg) and 2 free nuclei. T. tet- 

 raphylla (Romanov, 1938) is essentially similar. After the meiotic 

 divisions are over, 3 nuclei go to the micropylar pole and one to 

 the chalazal (Fig. 79A-D). All of them divide again (Fig. 79 E), 

 so that there are 6 daughter nuclei in the upper part of the sac and 

 2 in the lower. Cell plates are laid down at the conclusion of the 

 division, resulting in the formation of five cells at the micropylar 

 end (one of these is to be regarded as the egg) and one cell at the 

 chalazal, leaving 2 free nuclei (the polars) in the center (Fig. 79F). 



Since this peculiar mode of development occurs only in the 

 Eriostemones section of the genus Tulipa, it is known as the "Erio- 

 stemones form" of the Adoxa type. Other species of the genus 

 come under the Fritillaria or the Drusa type (see Maheshwari, 

 1948). 



10 Haque's (1950) observations on E. americanum and Walker's (1950) on U. 

 fulva, U. racemosa, and U. glabra show that the development sometimes follows 

 the Adoxa type and sometimes the Fritillaria type. 



