1422 A TEXTBOOK OF THEORETICAL BOTANY 



Both uninucleate and multinucleate cells may go to form the antipodal 

 complex, sometimes both types in the same sac, and the cells may either 

 form a compact chalazal tissue, as in some Gramineae and Gentianaceae, 

 or simply an irregular mass, as in Sparganinm. This genus shows multicel- 

 lular development probably at its maximum, as more than 150 antipodal 

 cells have been seen in one embryo sac. Multicellular antipodals are often 

 associated with antipodal haustoria, as mentioned below. 



Exceptional enlargement of the antipodal cells, without increase in 

 number beyond three, has been observed in several genera of Iridaceae 

 {Crocus, Iris, Gladiolus) and in a few other related Monocotyledons, e.g., 

 Narcissus, Ornithogalum, and Commelina. 



In some of these and other cases the enlargement is downward and may 

 be associated with invasion of the chalaza. In the Ranunculaceae, however, 

 the enlargement takes place upwards, into the embryo sac itself, which the 

 antipodal cells may largely occupy (Fig. 13 13 A). Enlargement begins 

 before fertilization but is often much greater afterwards and the big cells 

 may persist, even into the ripe seed. Hepatica differs from other genera of 

 the family in having a large group of antipodals, sometimes twenty-five 

 cells, which enlarge greatly after fertilization and become multinucleate, 

 as do also the three in Caltha and Aquilegia. There is evidence here of high 

 metabolic activity on the part of the antipodals, which is probably con- 

 nected with the nutrition of the embryo. 



Multiplication of nuclei within antipodal cells has frequently been 

 observed and also irregular fusions of nuclei in multinucleate cells. Nuclear 

 division is generally, probably always, mitotic. Observations of amitosis 

 are doubtful and are likely to be due to lobings and distortions of the nucleus, 

 which is often large and irregular in shape, another feature associated with 

 high metabolic activity, as in many secretory tissues. 



The arrangement of the three antipodal cells is very variable, but that 

 which simulates the micropylar group is the commonest, that is to say, two 

 cells occupying the base of the sac with one above them. The reverse of this 

 arrangement, hkewise linear groupings, both longitudinal and transverse, 

 also occur. 



We may summarize the variations of the antipodal apparatus as follows: 



1. Antipodals of free nuclei or separate cells, usually evanescent. (Some 



Orchidaceae, etc. See above.) 



2. Antipodals of three evanescent cells which may disappear before 



fertilization. (Salicaceae, etc. See above.) 



3. Antipodals of three relatively persistent cells, not remarkable for 



size or activity. (Many Metachlamydeae.) 



4. Antipodals of three persistent cells which become markedly enlarged 

 and active, especially after fertilization; sometimes multinucleate 

 and sometimes persisting into the seed. (Many Ranunculaceae.) 



5. Antipodals of an indefinite number of cells, forming a persistent 



complex, which grows and increases after fertilization and sometimes 

 persists into the seed. (Compositae, Gramineae, etc.) 



