ACROGENS. 100 



CHAPTER VIII. 



ACROGENS. 



Flower in the crannied wall, 



I pluck you out of the crannies, 



Hold you here in my hand, 



Little flower, root and all, 



And if I could understand 

 What you are, roots and all, and all in all, 

 I should know what God and man is. 



TENNYSON. 



1. IN the type of Acrogens the instinct of develop- 

 ment, or evolution of cells, is seen only at the summit 

 or apex of the stem. Cells in other parts of the plant 

 may enlarge, but do not multiply themselves. These 

 plants generally have distinct stems and leaves, with 

 stomata, (Chap. IV, Sec. n,) a certain amount of vascu- 

 lar tissue, (Chap. IV, Sec. 10,) and theca, or cases con- 

 taining spores. The Stoneworts, (Characcej) the Liver- 

 worts, (Hepaticce^) the Horsetails, (Equisetacecs^) the 

 Ferns, (Filices]) and the Mosses, (Musci^) are the prin- 

 cipal families of Acrogens. 



2. The Stoneworts (CHARACE^E) have generally been 

 regarded among Algae, or water-weeds. But they differ 

 greatly from Algse in having a distinct axis of growth, 

 and appendages. The axis may be a simple tube, (Ge- 

 nus Nitella^} or a tube with a cortical layer of smaller 

 tubes surrounding it, (Genus Chara^) They are found 

 in ponds and rivers, in tangled masses of a dull green 

 color. Each plant is hardly thicker than a stout needle, 



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