384 CLASSES OF ANGIOSPERMS 



and largest group of plants, where the sporophylls have become 

 highly modified and curiously associated in clusters called flowers, 

 more familiar names will be used in discussing them, i. e., ovule 

 for the megasporangium and its integument, stamen for micro- 

 sporophyll and pistil for megasporophyll. The terms "carpel" 

 and "pistil" are synonymous when these organs are distinct — 

 i. e., free from one another; but when they cohere to form a 

 compound pistil the term "carpel" is employed to indicate the 

 number of pistils that are united, as in the willow the pistil is 

 composed of two carpels, in the lily of three carpels, etc. 



While the sexual generation, mode of reproduction, and the 

 character of the tissues are very similar in all angiosperms, two 

 very distinct lines of variation or classes are to be noted : A, 

 the Monocotyledones, represented by the grasses, lilies and or- 

 , chids; B, the Dicotyledones, represented by our common trees, 

 roses, mints and daisies. 



Class A. Monocotyledones 



129. General Characteristics. — This group of angiosperms con- 

 tains about 25,000 species that constitute a very natural alliance, 

 owing to the uniformity and simplicity of their structures. These 

 features may be due to the uniform conditions under which these 

 plants live. The majority of Monocotyledones are moisture- 

 loving plants and are therefore exposed to very constant condi- 

 tions, which would naturally result in less stimulation and conse- 

 quent variation than in the case of plants exposed to the varying 

 conditions of drier soils. Some, to be sure, have become adapted 

 to dry and even arid regions, owing to peculiar modifications of 

 their leaves or stems, as in the grasses, certain bulbous plants, etc. 



The leaves are smooth and simple, lance-shaped or linear in 

 outline, sessile and often attached to the stem by sheathing bases. 

 The veins do not end in free branches on the margins of the 

 leaves, and as a result of this closed venation the leaves are usu- 

 ally entire and destitute of teeth or lobed margins. In many 

 instances the principal veins are quite parallel, but whatever the 

 arrangement, the prominent veins are connected by very minute 

 veinlets that form an inconspicuous network or reticulation 



