212 BIOLOGY. 



the tracheae increase for the first time to such a degree, 

 that they form a closed circle, the fibrous ring or zone of 

 wood. 



1074. The tracheae extend from one end of the plant 

 to the other ; many are wont to terminate only in nodes, 

 while these are to be regarded as arrested branches. 

 The air can therefore penetrate through the spiral vessels 

 from the leaves even to the apices of the roots. 



n. Anatomical Systems Sheaths. 



1075. These originate by vagination and separation 

 of the tissues in the transverse direction, and prevail 

 throughout the whole plant. The idea of the whole 

 vegetable structure is extremely simple. Originally the 

 plant is a vesicle in water, or cellular tissue in the seed ; 

 root and stalk also consist in their main bulk or propor- 

 tion of cellular tissue, which is called parenchyma. 

 Therein the three planetary processes reside inclosed. 

 Such a plant is still in the recognizable state of the pri- 

 mary organism. In the sequel, however, through the 

 influence of light, the polarity between light and dark- 

 ness issues forth in the parenchyma, the cellular tissue 

 obtains a linear direction, and becomes elongated into 

 spiral vessels. The spiral vessels form one or several 

 fasciculi, which emerge out of the parenchyma, by which 

 they, and each packet individually, are circularly sur- 

 rounded. The cellular tissue is as it were the soil, in 

 which the fasciculi of spiral vessels are rooted as proprie- 

 tary plants and out of which they grow. 



1076. The effort of the three vegetable processes, to 

 separate their organs from, and perfect them independ- 

 ently of, each other, is in incessant operation, both from 

 without inwards, as well as from above downwards, 

 because in both cases is light there, darkness here, dry- 

 ness there, humidity here. The cellular tissue, that has 

 finally become independent in the transverse direction or 

 from without inwards, is called hark, the self-substantial 

 tubular tissue is called liber, the non-dependent tracheal 

 tissue, wood. 



