FRILLS AND FUNDAMENTAL BAUS AS PLUMAGE CHARACTERS. 153 



At this point it seems necessary for the editor to supplement the above para- 

 graphs with a statement of what has been learned of the physiological basis of the 

 fundamental bars, and later to add a further word to the author's meager discus- 

 sion of this subject. The first of these objects will perhaps be best accomplished 

 by the following quotation (pages 356, 357) from our own publication: 20 



It has been shown that there exists in certain elements of the rapidly growing feather- 

 germ a rhythm of growth which is dependent upon the nutrition. Those parts of the 

 feather which are grown under the poorest nutritive conditions show defective structure 

 "fault-bars" of all grades of imperfection. Those regions of the feather normally 

 the larger part which are produced while growth and cell-division are more nearly in 

 full swing, form the "fundamental bars." 



In pigmented feathers, the development of pigment is modified at night along with 

 the other elements and there results a structurally weakened and less-pigmented area. 

 This region we have thus far spoken of as a fault-bar; since, however, this same area has 

 been found in some cases to lose considerable pigment without having lost any barbules, 

 we speak of it also as a "light fundamental bar." On the other hand, pigment develops 

 uninterruptedly during those hours of the day when growth is most rapid, and the well- 

 pigmented portion of the feather then laid down forms the "dark fundamental bar." 



Fault-bars and fundamental bars are universal in feathers (in white feathers there is, 

 of course, no rhythm of pigmentation), and are direct expressions of the rhythmic nutri- 

 tive 2I conditions. The poorest food conditions obtain at night. A reduced blood-pressure, 

 probably much emphasized in the later hours of the night, is to be regarded as a factor 

 (by affecting the nutrition) in the production of all fault-bars and of the light fundamental 

 bars, while the better normal nutrition of the day and of the first part of the night is asso- 

 ciated with the production of the dark fundamental bars. 



The large light and dark transverse bars with which we have all long been familiar 

 in Plymouth Rock fowls, in hawks, in jays, etc., are of course not the light and dark funda- 

 mental bars with which this work deals, and are not each the growth of a day or night; 

 it is perfectly evident that in them a single broad black or white bar may include the growth 

 of 2, 3, or more days. But even these broad bands of white and black may later be found 

 to bear secondary or derivable relations to the fundamental bars. 



The alternating light and dark fundamental bars are only rarely seen in their fullest 

 development, i.e., as well-defined alternating bands of lighter and darker color. Experience 

 would indicate that they are found to best advantage in pale feathers rather than in those 

 with a superabundance of pigment. ... It is, then, through such a mechanism as has 

 been described in the foregoing pages that the melanin pigment of feathers comes to be 

 laid down in alternating light and dark transverse bars. 



Several aspects of the occurrence, nature, and variation of this type of barring 

 are made clear by the following records and illustrations, all of which were prepared 

 by the author: 22 



20 Riddle, Biol. Bull., vol. 14, pages 328-370. 



21 The words "food" and "nutrition" are used in a general sense and include oxygen. It is not improbable that 

 the slower growth and cell-division, and the diminution of the production of melanin pigment under fault-bar-pro- 

 ducing conditions, are in part at least due to a reduced oxygen-supply. In all my experiments, and in every lowering 

 of the blood-pressure, the oxygen-supply of the tissues is diminished. The probability here stated grows in importance 

 when it is remembered that free oxygen plays an important rdle in the germination of seeds, the segmentation of ova 

 (mitotic activities), and probabl3' also in the oxidation (Samuely) of tyrosin (Gessard, v. Furth, and Schneider) to 

 form melanin. 



22 Much of the record on this subject was made before the cause of the barring was determined, and made, 

 therefore, with a view to obtaining light on this point. It seems necessary to present but little of this part of the 

 record. ED. 



