6 



and pressure of bees and of other insects upon the spot 

 caused a relaxation of the cell-walls, which became thereby 

 more permeable, and that more colored sap was attracted to 

 the stimulated spot. There was in the process no extra 

 heart pressure on the one hand, nor more root pressure on 

 the other. The flower being of one uniform color as stated, 

 the stimulus at one point would naturally draw some of the 

 colored sap from the neighboring- cells to that point, pre- 

 cisely as more red blood is drawn to an irritated spot simpl}" 

 because the caliber of the vessels is enlarged. 



The analogy therefore is, that local friction brings color 

 from the immediately surrounding parts, and that this addi- 

 tional color in l)oth plant and animal is confined exactly to 

 the limited s})ace which is irritated. Whether my analogy 

 (not his) is to be regarded as yalual)le or worthless will not 

 make the slightest difference to the main facts given regard- 

 ing the origin of the honey guide, which the critic com- 

 pletely ignores. 



I may be excused in extending these remarks somewhat 

 upon the subjects introduced by the reviewer. Undoubt- 

 edly the same irritation of the insects might, under some 

 circumstances, attract colorless sap, laden nevertheless with 

 pigmental elements, from which the chemical character of 

 the cell contents would develop color. If for instance the 

 cell contents of the petals should happen to be of a slightly 

 acid character, a certain color might develo[), while at the 

 same time if some of the same general sap should enter the 

 cells of another part or organ, as the stamens, whose cells 

 might chance to be slightly alkaline on account of their 

 special functions, these would l)e more than likely to de- 

 velop a different color. AVhether a flower is to ])e red or 

 blue may depend upon which of these elements prevail, and 

 how long it i)revails, for cell contents vary, and color varies 

 with them. The sap in Borracunacem is first strongly 

 acid, but as the flower develops, the acid disappears. The 

 flowers commonly change from red to blue. 



