346 FOURTH GROUP. SEED-PLANTS. 



Appendix. The CORDAITEAE. This group belongs to a type which existed in the 

 Carboniferous period, and cannot, as far as we know at present J , be united either with 

 the Cycadeae or Coniferae or Gnetaceae. Grand' Eury describes them as trees from 

 thirty to forty metres high, and branched only in the upper part ; the leaves were from 

 twenty centimetres to a metre in length, simple and unbranched, and from fifteen to 

 twenty centimetres broad. 



The male flowers were in cones inserted on the stem but not in the axils of the 

 leaves. The cones were composed of sterile and fertile leaves arranged spirally, 

 the fertile somewhat narrower than the sterile, and had at their apex three or four 

 microsporangia (pollen-sacs), which did not however hang down as in Gingko but 

 stood erect in the prolongation of the plane of the leaf. The macrosporangia 

 had two integuments and a ' pollen-chamber ' at the extremity of the nucellus, 

 as in the Cycadeae ; they were on long stalks which sprang several together as 

 branches of an axillary shoot from the axil of a bract, and were surrounded at their 

 base by a number of small leaves, like the female flowers of some of the Taxineae ; 

 these partial inflorescences appear to have been united into a spike-like general 

 inflorescence. The anatomical structure, on the other hand, of the stem and leaf shows 

 various points of agreement with that of the Coniferae. 



It is to be hoped that the recent discovery of the organs of fructification of the 

 Sigillarieae will enable us to determine whether those peculiar plants, which have been 

 hitherto ranked by many botanists with the Vascular Cryptogams, do really belong to 

 the Gymnosperms. 



II. ANGIOSPERMS 2 . 



The Angiosperms agree with the Gymnosperms in producing a seed, but differ 

 from them in the circumstance that the ovule is formed inside a chamber, the ovary , 

 and further in the processes of development which go on inside the embryo-sac 

 (macrospore). No prothallium bearing archegonia at its apex is formed in them 

 before fertilisation as in the Gymnosperms, but three naked cells are found at the 

 apex of the embryo-sac at the time of fertilisation, one of which is the oosphere ; the 

 nucleus of the embryo-sac lies in the middle of the sac, and its division after 

 fertilisation is the commencement of the formation of a tissue, which more or less 

 completely fills the embryo-sac and is known as the endosperm. The development 

 on the other hand of the pollen-grains or microspores is the same in all essential 

 points as that which takes place in the Gymnosperms. At the same time the 

 Angiosperms are distinguished from other Vascular plants by many peculiarities of 

 structure, especially in the formation of the flowers and fruit, in which the ordinary 

 morphological conditions suffer such peculiar changes and combinations, that a more 

 detailed account of them must be given before we proceed to describe the special 

 characteristics of the two classes. 



The Flower 3 . The flower of the Angiosperms is only occasionally terminal in 

 the sense, that the primary stem which is the development of the axis of the embryo 



1 Renault, Cours de Bot. fossile, premiere annee, Paris, 1881. [Heer in Bot. Centralbl. 1882.] 



2 The word is derived from the Greek dyytTov, a receptacle, and airep^a, the seed. 



3 The most complete account of the flower of the Angiosperms is to be found in Eichler's 

 Bluthendiagramme, I and II, Leipzig, 1875 and 1878, where the literature of the subject is also 

 very fully given. The most important work on the history of the development of the flower is 

 Payer's Traite d'organogenie de la fleur, Paris, 1857, with 154 splendid copper plates. [The ad- 

 mirable account of the flower given by Asa Gray in his Structural Botany (1880) should also be 

 consulted.] 



