THE FLOWER 285 



(covered by one or two indiisial 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 saproph^'tes. 



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 ])e elongated, glo])u]ar 

 or very short, or it may be flattened into a disk or hollow 



