340 DICOTYLEDON ES. 



[The Casuarinas differ from the ordinary Dicotyledons in many important 

 respects which may be briefly summarised thus : The bicarpellate $ -flower has 

 a well-pronounced stylar-cylinder terminated by two stigmas, but the cavity of the 

 ovary closes very soon after its formation, and in it are developed two parietal 

 ovules ; these are united by a bridge of cellulose to the styJar-cylinder or summit 

 of the ovary, and hence the ovules are connected with the walls of the ovary by 

 the bridge (above), as well as by the funicle (below). The archespore is developed 

 from the hypodermal cells at the summit of the nucellus, two primordial 

 mother-cells are first formed and from these by tangential divisions a central 

 cylindrical mass of cells (sporogenous-tissue) is produced which is surrounded 

 by tapetal cells. The cells of the sporogenous tissue correspond to the mother- 

 cells of the embryo-sac of other Augiosperms ; they divide transversely and 

 from 16-20 macrospores are formed together with inactive cells which are not 

 crushed together as in the case of other Phanerogams. The sexual apparatus 

 is developed from a single cell, but the number of cells compo-iug this appar- 

 atus is subject to variation, the oosphere being accompanied by one or two 

 neighbouring cells which resemble canal-cells rather than syiiergidte. The 

 sexual apparatus is found in the majority of the macrospores, but in most of 

 these it remains as a number of .naked cells ; while in the fertile macrospores 

 the cells are invested by walls of cellulose (usually only one fertile macrospore is 

 found in each ovule). Antipodal cells are never developed. The macrospores 

 elongate considerably towards the chalaza, into which some penetrate. The 

 pollen-tube traverses the stylar cylinder and enters the ovules at the chalaza, 

 its passage through the the tissue of the nucellus being assisted by the pro- 

 longation of the macrospores. About the centre of the nucellus the pollen- 

 tube is ruptured ; the apical portion which alone takes part in the fertilisation 

 being firmly attached to the macrospore. Although the actual impregnation 

 has not been observed, Treub considers that the endosperm begins to be 

 formed before fertilisation.] 



Family 3. Querciflorae. 



Trees and shrubs with small, unisexual, monoecious flowers, 

 having no perianth or a simple inconspicuous one. The <$ and ? 

 flowers are very different and generally placed in separate inflor- 

 escences. The ^-flowers are most often adnate to the bracts. The 

 stamens are placed opposite the perianth-leaves, when they are pre- 

 sent in equal numbers. The $ -flower is naked, or has a superior 

 perianth. The ovary at the base is 2 or 3-(-6) Jocular with 1 or 

 2 pendulous ovules in each loculus, only one of which is developed ; 

 the fruit is a one-seeded nut ; endosperm absent ; embryo straight. 

 The inflorescences, which are either compound and mixed (small 

 dichasia in spikes) or simple, are here also termed catkins] but, 

 strictly speaking, this term is applied to the <$ -inflor-escences only. 

 In all Querciflorse the leaves are scattered (usually in 2 rows) 

 simple, and penninerved, and with deciduous stipules. 



