THE DICOTYLEDONES 



1765 



The genus Almis contains twenty-five species which occur in the north 

 temperate zone and in the Andes. A. ghitinosa (Alder) (Fig. 1649) is common 

 as a riverside British tree. Peculiar masses of coralloid rootlets are often 

 found on the roots, which are stated to be caused by an organism Schinzia 



Fig. 1649. — Alniis gliitinosa. Alder. Long 

 male and short female catkins. 



alni w'hose nature is uncertain, though it is probably related to the Actino- 

 mycetes. A symbiotic relationship has been postulated. 



Another order which shows certain affinities with the Fagales is the 

 Casuarinales. '1 his is a small order containing the single family Casua- 

 rinaceae with the single genus Casiiarina. The genus is widely distributed 

 throughout the drier parts of Australia and Polynesia. Some thirty-five 

 species are recognized. The plants are trees (Fig. 1650) composed of long 

 slender branches which only produce whorls of scale leaves like those of 

 Equisetiim. The stems (Fig. 165 1) are assimilatory and the cortex is deeply 

 grooved, the chlorenchyma and stomata being distributed in the grooves in 

 a way resembling that in Cytisus. The ridges are composed of thickened 

 sclerotic cells giving the whole plant a markedly xeromorphic character. 



The flowers are unisexual. The male flowers (Fig. 1652) are borne in 

 terminal spikes on lateral branches. In these spikes the internodes are 

 very short and the nodes are surrounded by cups formed from bracts, 

 inside which are several stamens. Each is regarded as representing a male 

 flower composed of one stamen with a two-leaved perianth and two 



