422 Journal of Agricultural Research voi. xin, no. s 



SECRETIONS OF THE INTERNAL GLANDS 



Microscopical investigations of the secretion of the internal gland have 

 shown the presence of a variety of substances and also of differences of 

 content, according as the glands are or are not exposed to the action of 

 light. Most evident are a deep-red pigment iand a yellow or brownish 

 oily-appearing substance. The red, or sometimes purple, pigment is 

 deposited in amorphous semisolid or in liquid form within the flattened 

 layers of the glands of illuminated parts. It is most prominent in the 

 glands of the young green parts, and its density accounts for their "black" 

 appearance; the red coloration may be made microscopically evident by 

 crushing the gland, thereby diluting the pigment in cell sap. The coloring 

 of conspicuous red spots on cotton foliage often originates in wounded 

 glands. No red pigment is normally formed in the glands of the seed or 

 secondary cortex. A small amount is usually developed in the glands of 

 the cotyledon when the latter becomes functional as a leaf. Pigment is 

 first formed in the glands of the petals as the latter protrude from the bud. 



This red pigment gives the reaction typical of anthocyans. It is solu- 

 ble in water and alcohol, nearly insoluble in ether, and insoluble in petro- 

 leum ether. Acids dissolve it with a brilliant red coloration. Green or 

 blue colors are first formed with alkalis; strongly alkaline solutions are 

 soon decolorized. Basic lead acetate forms a dark-green precipitate. 

 Iron salts cause a blue or purple coloration. The red pigment of the 

 glands is apparently more strongly developed in G. harhadense than in 

 G. hirsutum. If a young leaf of the former species be slightly crushed, 

 the diffusion of anthocyan may color the whole injured area a brilliant 

 red. 



The content of the central chamber of the gland varies from a yellow 

 oily fluid in the young gland to a resinous-red solid substance in the ma- 

 ture gland of the seed. With proper reagents the yellow secretions of 

 the glands exposed to light are seen to differ in character from those of 

 the inner cortex of the stem, root bark, seeds, and the partially devel- 

 oped corolla, which, by their positions, are shielded from the influence of 

 Hght. 



SECRETIONS OF THE GL.^NDS EXPOSED TO LIGHT 



In the large glands of the boll occurs a bright-yellow oily substance 

 in which may be intermixed granular fragments of a dull-yellow or 

 orange color. In the smaller glands of other outer portions of the 

 plant the yellow substance occurs in smaller amount; the solid some- 

 times predominates. Reactions show the solid, in the main, to be a con- 

 densation product of the yellow liquid. The liquid, which flows out in 

 globules as the gland is cut, is nearly insoluble in water and is not 

 readily emulsified in it. It is very soluble in ethyl and methyl alcohol, 

 acetone, chloroform, and ether, forming a bright-yellow solution. It is 

 almost or quite insoluble in petroleum ether and xylene. In most acids 



