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 

 (33, 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 ) . ARCHEGONI ATAE : Sporophyta in which the egg-organ 

 is present and functional. 



(3). METASPERMAE : 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, puff- 

 balls, etc. 



Examples of the Archegoniatae are such algae as Chara and 

 Nitella, the liverworts, mosses, ferns, pillworts, club-mosses, 

 scouring-rushes. Sigillarias, Lepidodendrons, quill worts, 

 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). 



(34) MacMillan: Sexual Immobility as a Ciusefor the Development of the Sporophyte, 

 Amer. Nat. xxv. 22-25 (1891). 



(35) Campbell: Relationships of the Arcliegoniata, Bot. Gaz. xvi. 323-333 (1891). 



(36) MacMillan: Suggestions on the Classification of the Metaphyta, Bot. Gaz. xvii. 

 108-113 (1892). 



