170 PHYSIOLOGICAL BOTANY. 



globe of about thirty-five degrees both sides of the 

 Equator. It flourishes in the bare sands of the sea- 

 coast, skirts arid plains, beautifies the oasis of the 

 desert, and inhabits the murky bottoms of southern 

 swamps and low islands of Southern Asia and tropical 

 America. These plants are of vast utility, producing 

 food and many domestic and economic products. 



There are certain noticeable things in the mode of 

 monocotyledonous growth. The stem has no proper 

 bark, does not increase in diameter after it is perfectly 

 formed, and, with few exceptions, consists of an un- 

 branched cylindrical column, made up of pith inter- 

 mingled with fibro-vascular threads, generally without 

 any order of arrangement, the whole inclosed in a 

 rind or false bark (521-524), well illustrated in a 

 cross-section of a stalk of Indian Corn. There are a 

 few plants that seem to be connecting links between 

 these two modes of growth ; a notable example of 

 which is Dracaena draco, or Dragon-tree, which has a 

 cambium region, and continues to increase in diameter. 



Formerly these plants were called Endogens, meaning Inside growers, 

 in contradistinction to Exogens, or Outside growers, because the new ma- 

 terial of growth was then supposed to be deposited always inside of the last 

 deposit of woody bundles ; but as it is now known that the additions are 

 interspersed among the former ones, in most cases without special order, the 

 name is not expressive. Plants of this mode of growth have but one cotyle- 

 don, or seed leaf ; their flowers are mostly three-parted, and their leaves 

 generally parallel- veined. See Monocotyledons, pages 168-170. 



423. Tissues of the Pteridophyta. The Ferns and 

 their allies have a complicated and well-marked organi- 

 zation ; the outer bark is similar to that of the flower- 

 ing plants, and vascular-woody fiber extends through- 

 out the stem, and leaf stalks ramifying in the fronds, 

 to which the great beauty of this division of the 

 vegetable world is due. 



