Stockard : Nectar-glands of Vicia Faba 251 



will be red while the lower cell-layers are blue. Again, layers of 

 red and blue cells may alternate for as many as four or five layers 

 or rows. The contents of the hair-cells are actually at times of 

 different colors, the distal pair being red or blue while the proximal 

 pair are, conversely, blue or red. In mature glands many of the 

 outer tips or distal cells of the nectar-hairs contain a colorless 

 liquid. Thus the cell-contents lose their pigmentation before being 

 thrown out. Often the entire gland is found to be of one color, 

 either blue or red. 



This shifting color-scheme suggested to me that possibly the 

 color depended upon the conditions of acidity or alkalinity in the 

 different cells. Therefore experiments were tried in which acid 

 and basic solutions were passed over the glands while on the slide 

 and the responses proved that the color did depend upon the cell's 

 chemical reaction. When a weak HC1 solution was passed over 

 a gland containing alternate rows of blue and red cells all the blue 

 cells became red, just as litmus would respond to acid. If dilute 

 NaOH was now applied until the liquid on the slide became alka- 

 line the cells all changed to blue. One is able to alternate this 

 color-change back and forth for a number of times, provided the 

 acid solution is not allowed to remain for too long a time, as the 

 cell-substance is soluble in it, finally dissolving out. This sug- 

 gests Bonnier's statement that an invertin which dissolves the 

 secretion-products is to be found in glands, and Lloyd also sug- 

 gested that this invertin might occur in certain non-green cells in 

 the pericycle of Pteridium nectar-glands. In the glands of Vicia 

 Faba the nuclei in most cases also become red on meeting the acid 

 and thus indicate that they contain material similar to the secretion- 

 substance. On adding the base the nuclei became clear and diffi- 

 cult to see having lost their pinkish acid response. 



Testing with Fehling's solution for the variety of sugar present 

 in the secretion substance, cane sugar was found. 



HISTOLOGY AND DEVELOPMENT 



A. Structure. — Studying these glands as stained preparations, 

 one sees very little histological difference between the cells of the 

 gland-area and those in adjacent parts of the stipule. The deeper 

 layers of cells in the gland are strikingly similar to cells of the 



