16 MORPHOLOGY OF THE ANGIOSPERMS 



other, the dicotyledons have the most primitive stipules. Evidence from 

 nodal structure, from seedlings, and from comparison in related taxa 

 indicates that the free stipules are the more primitive form. The many 

 traces of the monocotyledon-sheath margins suggest advanced structure. 

 (The multilacunar node is generally recognized as an advanced type.) 

 Seedlings in some monocotyledons show progressive stages in their early 

 leaves from paired free stipules to sheathing leafbases — Potamogei^on. 

 Free paired stipules are present in Potamogeton densus, in species of 

 Ruppia, Althenia, Najas, Hydrocharis, Smilax. Increasing adnation of 

 free stipules is seen in many dicotyledonous families — Rosaceae, 

 Leguminosae. Fused adnate stipules and sheathing leafbases are fre- 

 quent in dicotyledons, rare in monocotyledons — Zannichellia palustris. 

 The theory that free basal stipules are the primitive type seems best 

 supported by evidence of all types. In stipular type, the leaves of the 

 dicotyledons are more primitive than those of the monocotyledons. 



On the basis of the theory that paired lateral stipules are primitive, 

 two views have been held as to the relationship of the free and the 

 adnate. It is claimed that the free stipules stood at first at the base of 

 the petiole; that a change to a free (cauline) position came later as 

 the leaf buttress matured and displaced them. The other view is that 

 the position of the free stipules is the primitive one in the shoot, that a 

 closer relation to the leaf is an advanced character. Ontogenetic evi- 

 dence can be found to support each of these views; to determine the 

 ancestral position of the stipules, evidence from ontogeny alone is not 

 sufficient. 



Small, reduced leaves borne close to the base of lateral branches 

 have long been termed prophyUs. They have also often been called 

 hracteoles, though this term is usually restricted to inflorescences and 

 flowers. Commonly, there are two lateral prophylls in the dicotyledons 

 and one in the monocotyledons. Where there are two prophylls, they 

 may stand "opposite," forming a pair, or one may be distal to the other. 

 Definitions of prophylls emphasize their position in relation to leaves 

 on the branch; they do not fit into the phyllotactic spiral of the branch. 

 It is apparent that they do not when the pairs are opposite but 

 when one prophyll is above the other, they commonly seem to fit into 

 the spiral. 



The numerical distribution of the prophylls — two in the dicotyledons 

 and one in monocotyledons — has sometimes been considered significant, 

 because it seems to parallel cotyledon number, but there are many ex- 

 ceptions. In inflorescences, prophylls may be prominent organs, espe- 

 cially on the ultimate branchlets, and even on the pedicles, as in the 

 Cyperaceae. (Here they are commonly called bracteoles.) 



The solitary prophyll is usually superaxillary, with its ventral side 



