CONSTANCE: SYSTEMAJICS OF THE ANGIOSPERMS 431 



rium, because Casuarina shows this peculiarity, has been made much of by those 

 seeking to establish a close connection between gymnosperms and "the Amen- 

 tiferae" (Engler, Zimmermann, Iljelmqvist), but faith in its evolutionary sig- 

 nificance appears to have declined (Maheshwari, 1950). 



The mode of development within the ovule and the entrance into the female 

 gametophyte of the pollen tube, whether endotropic and chalazogamous or ecto- 

 tropic and porogamous, has been accorded major importance in the past. Indeed, 

 Engler's initial placing of Casuarina at the very beginning of the dicotyledons 

 was largely based on the belief that chalazogamy is a primitive feature affording 

 unquestionable relationship between higher gymnosperms and ''the Amenti- 

 ferae," a view supported at least in part by K. Fritsch (1905), Wettstein, Zim- 

 mermann, Hjelmqvist, Janchen, and Suessenguth and Merxmiiller. The sub- 

 sequent discovery that chalazogamy occurs sporadically in various groups of 

 angiosperms, and that the course of pollen-tube growth appears to be determined 

 physiologically rather than phylogenetically, has resulted in considerable de- 

 emphasis (Maheshwari, 1950). 



B. Female gametophyte: While these and other features of the o\n.ile have 

 been drawn upon for taxonomic and phylogenetic purposes, the focus of atten- 

 tion has long been upon the female gametophyte. "The origin of the embrj-o 

 sac remains today," as recently affirmed by Battaglia, "one of the outstanding 

 problems of Angiosperm evolution" (1951, p. 87). The several interpretations 

 extant seek to explain the angiosperm structure by derivation from the arche- 

 gonia-bearing female gametophyte of gymnosperms. The discovery of Hof- 

 meister and Strasburger of striking resemblances between the gametophytes of 

 some Gnetales — two genera of which likewise lack arehegonia — and those of flow- 

 ering plants was interpreted as a confirmation of the phylogenetic views of 

 Engler and Wettstein. Battaglia, in proposing his "Archegonial Disappearance 

 Theory," states that "an archegonial homology between angiosperms and gymno- 

 sperms does not exist" (1951, p. 90), and he, Schnarf, and Maheshwari agree in 

 regarding the situation in Gnetales as merely parallel with, and not genetically 

 related to, that prevailing in angiosperms. 



The uniformity of mature embryo-sac structure in angiosperms has been 

 widely offered as a compelling argument for their monophyletic origin (Bessey, 

 Sargant, Parkin, Schnarf; Maheshwari, 1939; Copeland, 1940; Fagerlind, 1946; 

 Johansen, 1950; Whitehouse). Joshi (1938), Turrill (1942), and Gaussen 

 (1952), however, have interpreted the occurrence of embryo sacs of different 

 development and ultimate configuration as evidence suggesting polyphylesis 

 of the group. Some ten different (sexual) embryo-sac types are distinguishable 

 on the basis of the number of megaspores from which they take their origin 

 (mono-, bi-, or tetrasporic), the number of cell or nuclear divisions intervening 

 between initiation and maturity, and the number and arrangement of com- 

 ponent cells or nuclei when fully formed (Maheshwari, 1937, 1945, 1948, 1950; 

 Battaglia). That the monosporic, eight-nucleate Normal or Polygonum type is 

 primitive for the angiosperms has been generally maintained, because it has 

 the largest number of nuclear divisions, spore formation and embryo-sac devel- 

 opment are well separated temporally, it is the most common type — in some 70 

 per cent of angiosperms thus far investigated, according to Maheshwari — and 

 because all other types can be derived from it (Sargant, Lotsy, Parkin, Engler, 



