THE FLOWER 285 
(covered by one or two indusial coats) now becomes the 
“seed.” Upon germination of the seed the sporophyte 
escapes, sending its roots downward into the soil, and 
its stem upward into the light, bearing green (annual 
or perennial) leaves. 
513. The tissues of the Flowering Plants show a higher 
development than in any of the preceding phyla. 
They range, in size and duration, from herbs, a few 
millimeters in extent and living but a few days or weeks, 
to enormous trees, 50 to 100 meters high and many 
centuries old; they live in all kinds of habitats from very 
wet to very dry, and from the most protected to the most 
exposed situations; accordingly their tissues, especially 
those which are supporting and conducting, show all 
degrees of variation from very simple to the most com- 
plex. The supporting and conducting bundles are here 
frequently united into fibrovascular bundles, which in the 
higher forms remain ‘‘open” and are arranged in a cyl- 
inder in the stem, thus providing a cambium zone for 
the thickening of the perennial stem. 
514. Most Flowering Plants are terrestrial and chloro- 
phyll-bearing; there are, however, many aquatic and 
aerial species, and a considerable number of parasites 
and saprophytes. 
515. A Typical Flower. Flowers have so many par- 
ticular forms that it would be impossible to describe 
them here, and yet they all conform to a general plan of 
structure. In other words, each particular flower shows 
a greater or less modification of or departure from what 
may be called the typical structure. 
516. First of all, every flower has a central stem por- 
tion (axis), on which there grow pistils, stamens, and a 
perianth. This flower axis may be elongated, globular 
or very short, or it may be flattened into a disk or hollow 
