INTRODUCTION. 21 
than such algae as Oedogonium. A discussion of the conditions 
under which the Sporophyta probably originated and notes on 
their classification may be found in recent periodical literature 
(88, 34, 35, 36). It may be well to say that all of our subject- 
matter, in the following list is purely sporophytic. 
Continuing our classification of the vegetable kingdom, it 
will be found that we may again divide the Sporophyta into 
three alliances based upon the manner of development of the 
egg-organ or archegonium. This organ combines the func- 
tions of an ovary and uterus as commonly recognised in 
the mammalia. That is, it produces the egg, during the differ- 
entiation and maturation of its cellular structure, and it retains 
the egg as within a pouch, nourishing it through at least its 
first segmentations after fertilisation in view of which the egg 
developes as an embryo sporophyte. We may distinguish, then, 
the three following alliances of the Sporophyta: 
(1). THALLOPHYTa: Sporophyta in which the egg-organ is 
not developed as a protective structure about the egg and in 
which there are no accessory characters that indicate an ances- 
tral line containing egg-organ-producing progenitors. 
(2). ARCHEGONIATAE: Sporophytain which the egg-organ 
is present and functional. 
(3). MBETASPERMAE: Sporophyta in which the egg-organ 
is aborted and no purely vegetative cells are to be found in 
either the male or female plants. 
Examples of the Thallophyta, which is here defined in the 
narrower sense and does not include the Gamophyta or Proto- 
phyta—as is more customary—are to be looked for among the 
sea-weeds, fresh-water algae and especially among the higher, 
spore-fruit-producing. fungi, such as the mushrooms, puft- 
balls, ete. 
Examples of the Archegoniatae are such algae as Chara and 
Nitella, the liverworts, mosses, ferns, pillworts, club-mosses, 
scouring-rushes. Sigillarias, Lepidodendrons, quillworts, 
cycads, pines and other conifers, and joint-firs. Transitional 
forms occur in the region of Gnetum, Ephedra and Casuarina 
leading over to the third and highest class of plants—the 
Metaspermae. 
(33) Bowers: Homologous and Antithetic Alternation, Ann. of Bot. iv. 347-370 (1890). 
(31) MacMillan: Sexual Immobility as a Cruse for the Development of the Sporophyte, 
Amer. Nat. xxv, 22-25 (1891). 
(35) Campbell: Relationships of the Archegoniata, Bot. Gaz. xvi. 323-333 (1891). 
(36) MacMillan: Suggestions on the Classification of the Metaphyta, Bot. Gaz. xvii. 
108-113 (1892). 
