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CHAPTER XVI 
PHYLUM X. CALAMOPHYTA 
THE CALAMITES 
463. As far as we know them the Calamites are green 
plants in which the marked difference between the small 
gametophytes and the large sporophytes seen in the 
Ferns is continued, but here the sporophyte stems are 
mostly hollow and jointed, and the leaves relatively 
small. A great difficulty in studying the plants of this 
phylum is that although common in the Paleozoic 
period, but few (about 24 species) have survived to the 
present time, and our knowledge of them is confined to 
what we have been able to make out fram fragmentary 
fossils, helped out in some details by a study of the 
surviving species. 
464. This much, however, has been made out pretty 
certainly: Gametophytes small, and short-lived, mostly 
monoecious; Sporophytes large, long-lived, with roots, 
and elongated, cylindrical, jointed, often hollow stems, 
bearing relatively small whorled leaves at the joints; 
spores alike (isospores), or of two kinds (heterospores), 
borne in cones of sporophylls (i.e. special spore-bearing 
leaves). 
465. Like the Ferns the Calamites have well-developed 
tissues in the sporophyte generation; the vascular 
bundles are of a higher type (‘‘collateral”), and are 
arranged in a cylinder in the stem. When these bundles 
are “‘open”’ the stems have the power of increasing in 
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