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318 Je tructural ey Physiological Botany, H, oid 
in which the leaves.are formed, and on the verticillate ar- 
rangement of the branches which spring from buds in the 
cortex (Fig. 443). While, in respect of their vegetative 
organs, they can be compared only with the Australian 
Fic. 443 II.—A peltate scale bearing the sporangia on its inner side facing the stem, 
five being visible (magnified) ; III. spore with the elaters unrolled which were 
previously coiled spirally round it (greatly magnified) ; IV. &. fuviatile ; rhi- 
zome covered everywhere with root-hairs, and having four tubers about the size of 
hazel-nuts which would, under favourable conditions, develope into new stems. 
dicotyledonous Casuarineze and the extinct Calamites, in 
their mode of reproduction the Equisetaceze closely resemble 
Ferns. In the internal structure of the stem the azr~-cavities 
are of great importance. Its centre is occupied by a large 
central air-cavity (Fig. 444 A, c); and in the surrounding 
ring of tissue, which is often rather narrow, there is almost 
always a cortical air-cavity (Fig. 444 A, 7) between each — 
ya 
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