242 GENUS ATRIPLEX. 



when it occurs in pistillate flowers. It has been found only in hortensis, dioeca, monilifera, 

 and phyllostegia, all of which exhibit other features of a primitive nature. In phyllostegia 

 the perianth may be either present or absent, even in flowers of the same plant, and vari- 

 ous degrees of suppression have been noted (see table 25, p. 269). 



Fruiting bracts. — These structures have been almost universally considered as modified 

 upper leaves. Evidence for this belief was given by Moquin-Tandon (Chenop. Enum. 

 1840), and recently the case has been stated by Collins (U. S. Dept. Agr. Div. Bot. Bull. 

 27:10, 1901). After reviewing the Australian species, Bentham (Fl. Austral. 5:166, 

 1870) came to the conclusion that the so-called bracts were homologous with the male 

 perianth. The regular occurrence of an undoubted perianth between the bracts and the 

 pistil in several of the species {hortensis, dioeca, phyllostegia, the first the type of the 

 genus) clearly demonstrates that the structures under consideration are true bracts and 

 not a part of the flower proper. This view was later adopted by Bentham (in Bentham 

 and Hooker, Gen. PI. 3:53, 1880). 



More reliance has been placed upon the bract characters by nearly all writers on the 

 genus than upon any other set of criteria, and very much more than their value warrants. 

 The bracts vary to so great an extent that the extremes seem to present ideal criteria for 

 the recognition of species. But over and over again these extremes are found on indi- 

 vidual plants, not in such a manner as to indicate hybridization, but rather as a mark of 

 variation between the individual bracts. Thus, smooth to strongly tuberculate or long- 

 appendaged bracts very frequently are found on single plants of some species, as also are 

 both sessile and long-stalked ones. Examples of this are shown in some of the illustra- 

 tions (plates 41, 43, 44). Many more are mentioned in the descriptions of the species and 

 subspecies and under the minor variations. It is, of course, possible that such qualities 

 as those just mentioned are heritable and that the mingling of different types of bract 

 on the same plant is merely the outcome of a heterozygous condition. If this is the case, 

 then the utilization of such features for purposes of classification is futile, unless all of the 

 forms are first subjected to a close genetical analysis, and at present this would serve no 

 useful purpose. The grouping of these minor variations into closely defined subspecies 

 and species will provide a classification adequate to all ordinary needs. An alternate ex- 

 planation of these variations is that they are ecologic and perhaps correlated with the 

 food-supply. This probably is the case when variation occurs in the same small cluster or 

 between the bracts of a single pair, as often happens. In Atriplex parishi it has been 

 noted that in some plants the upper bract of each pair, that is the one facing the stem, is 

 always muricate, whereas the bract facing downward toward the subtending leaf is 

 always smooth. The significance of this is not known. 



Although the sculpturing of the bracts and the length of their stalks are characters of 

 but little- value, much use can be made of certain other features connected with these 

 structures. Often the size is so different in even closely related species that this may be 

 safely employed as a criterion. Only fully mature bracts should be measured for this 

 purpose. The size character would be more definite if the dimensions of the body, 

 exclusive of appendages, wings, or free margins could be determined, but this seems 

 impracticable. It is therefore sometimes necessary to make allowance for unusual sur- 

 face outgrowths. An extreme case of variation in the size of bracts is illustrated in 

 figure 31 (p. 252). The shape is also helpful. It is assumed that the bracts in primitive 

 forms were broadest below the middle, as in ordinary foliage leaves, and that bracts 

 broadest near or above the middle are indicative of derived groups. United bracts are 

 more highly specialized than distinct ones, since these structures are modifications of 

 distinct leaves of the inflorescence. The extent of fusion is helpful in working out phy- 

 logenies, but it is difficult to express in the form of a proportion, since the thin margins, 

 often unequally toothed, should first be eliminated. Bracts of ordinary leaf-like texture 



