B. Spermatophyta «+ Seed Plants. 
Terrestrial or aquatic plants usually with green foliage, 
extremely varied in habit, ranging from tall trees to 
z aa 
minute herbs, usually with aerial stems, As in the 
ferns reproduction is indirectly accomplished by spores 
which are of two kinds, the microspores (pollen) being 
produced within the stamens which are considered to be 
modified leaves, the single megaspore being formed 
within a structure termed the ovule which it never 
leaves, The ovules are produced either upon the sur- 
face of modified leaves (in the gymnosperms) which are 
4 usually assembled into. a cone, or are produced within 
| the cavity formed by the union of one or more modified 
leaves termed the pistil (in the angiosperms). The 
4 stamens and pistil or pistils are assembled variously 
into a structure known as the flower, which (in the 
angiosoerms) is commonly surrounded by one or two 
series of modified leaves termed the calyx and 
corolla, The extremely varied arrangement of the parts of 
. the flower and the nature of the seed and fruit are the 
bases of classification, 
