GROUP IV. — PHANEROGAMIA : DICOTYLEDONES : MONOCHLAMYDE^. 585 



Order 6. Casuarinace^:. Trees having somewhat the appearance 

 of Horse-tails (Equisetum), with long channelled internodes, and 

 leaves forming a toothed sheath. The mona'cious flowers are in 

 distinct catkins; the c? flowers consist of a single axial stamen 

 (see p. 78) and two perianth-leaves : the ? of a dimerous uni- 

 locular ovarj invested by two bracteoles, v^hich, when ripe, are 

 hard and woody ; the whole ? catkin then resembles a pine-cone : 

 ovules, generally two, orthotropus, ascending. (For peculiarities 

 of fertilisation, etc., see p. 528.) 



Several species of Casuarina are iadigenous in Australia. 



Order 7. Salicacej:. The dioecious flowers are arranged in 

 amenta, and they are borne in the axils of the bracts without any 

 bracteoles. There is no 

 perianth, but each flower 

 contains a glandular disc 

 or nectary. The ovary is 

 dimerous and unilocular, 

 and contains a number of 

 parietal ovules. The de- 

 hiscence of the fruit is 

 loculicidal ; the numerous 

 seeds are furnished with 

 a pencil of silky hairs at 

 their bases (p. 459). The 

 catkins are developed at the ends of lateral dwarf-shoots which 

 always bear scales or even a few foliage-leaves. 



Salix, the "Willow or Sallow, has entire bracts, a one or two-toothed nectary 

 in each flower, and usually two stamens, entire shortly- stalked leaves, and its 

 winter-buds are covered by a scale which is formed bj the coalescence of two. 

 The shoots, which grow throughout the summer, die down yearly. Some species, 

 such as S. aiha, fragilis, and hahylonica, the Weeping Willow, have pendulous 

 branches, and are arborescent : most of them are shrubby, and some, puch as 

 .S'. reticulata, retusa, and herbacea are small decumbent shrubs occurring in the 

 Alps and in high latitudes. In S. purpurea and iucana the two stamens are 

 connate : .S*. triandra has three stamens. Most of the species grow on the banks 

 of rivers ; S. aurita and caprea in forests, and S. repeus and others on moors. 



Populus, the Poplar, has toothed or lobed bracts, a cup-shaped nectary (Fig. 

 390 C,p), and numerous (4-30) stamens ; the leaves are often lobed and have 

 long petioles ; the winter-buds are enclosed by a number of scales ; the shools 

 have a terminal bud. In the Section Leuce tlie young shoots are pubescent, 

 and the buds are not viscid ; the <J flowers have usually only from 1-8 stamens, 

 and the stigmata have 2-4 lobes : to this section belong P. alba, the White 



