Formed Constituents of Organisms 163 



world, and we believe are primarily defensive. They occur 

 here and there amongst the algae and fungi, are fairly abundant 

 in the moss and fern alliances, become at times very abundant 

 in the cellular cortex of many gynmosperms, they are fairly 

 frequent, sometimes even rich, in the aerial and subterranean 

 parts of monocotyledons, but attain their richest and most 

 abundant formation in the dicotyledons, whose underground 

 and aerial stems, leaves, and fruits may contain relatively 

 large quantities. Czapek has presented (^-4, 2: 587-591) the 

 views held by different investigators as to the functions of the 

 tannins. According to some they are end-products in analytic 

 action; others consider that they aid in food transformations; 

 or again that they unite ^ath definite bodies to form new com- 

 pounds; or, as we would most fully accept, they are primarily 

 protective compounds, that are usually massed in or near the 

 surface tissues, where attack by other organisms is often made. 



There now remain for consideration certain structural and 

 physiological conditions that can best be treated in succession 

 to what has gone before. 



Alike in plants and animals glandular secreting structures 

 are identical morphologically, and may range from a single 

 cell, \\-ith richly granular protoplasm and a well-formed nucleus, 

 through every grade of complexity till we reach the elaborate 

 sunken glands that are formed on the stem and leaves of the 

 pitcher-plants or Nepenthes (78: 17), and the similar glands 

 along the alimentary canal of animals (70, 7: 270; 10: 12). 

 But amongst the liighest animals, owing to the softness of 

 surrounding tissues, the rich nerve supply, and the abundant 

 secretion of some glands, these have advanced in branching 

 complexity, though by no means in fundamental relation, 

 far beyond the condition shown by the simpler animal glands. 



That the secretion of such glands, whether of a simple or 

 of a comi)lex nature, is a restricted and locally evolved feature 

 is shown on adjoining faces of the same tissue. Thus in Nepen- 

 thes one may at times observe a sugar-excreting gland on the 

 outer side of the pitcher wall, and a tryptic-excreting gland 

 on the inner side, both being connected mth a common bundle 

 that ramifies through the separating tissue. In animals from 

 the cyclostomes upward, and even amongst many inverte- 



