THE PLANT BODY 15 



probable, the primitive angiosperm leaf should be stipulate. The primi- 

 tive Helobiales fit into this picture, as do the Magnoliaceae and a few 

 other woody-ranahan taxa, but other woody-ranalian hues are without 

 stipules. 



Stipules have been interpreted as basal leaflets of a compound leaf 

 and as remnants of an ancestral whorl of leaves, but neither ontogeny 

 nor anatomy supports these views, and, in angiosperms, whorled leaves 

 represent advanced phyllotaxy. The stipules of the gymnosperms and 

 ferns (except perhaps the Eusporangiatae) are not nodal appendages. 



Prolongations of the stipulate margins beyond the median part of 

 the sheathing base of monocotyledon leaves form a more or less free 

 structure, the ligitle. The ligule may be a two-lobed or two-toothed 

 structure, or a simple structure where the two parts are united as a 

 ventral "collar." (This collar may become greatly enlarged and form 

 an important part of the leaf. ) Formed in this way, a ligule is obviously 

 stipular in nature, but the interpretation of the ligule has been expanded 

 to cover the basal sheath, with which the ligule is continuous, and the 

 entire sheath called the ligule. This understanding of the ligule has 

 brought about great confusion in the interpretation of the monocotyle- 

 donous embryo (Chap. 9). The ligule is not morphologically distinct 

 from the stipules, of which it usually represents the distal part. (A 

 descriptive distinction becomes necessary only in the interpretation of 

 the coleoptile of the grasses and some other families where the coleoptile 

 is called "ligular." The coleoptile is a part of the sheathing leafbase, not 

 of the ligule.) Ligules are present not only in many monocotyledons 

 but also in some dicotyledonous families — Droseraceae, Saxifragaceae, 

 Araliaceae, Piperaceae. The ligule, or hastula, of the palms represents a 

 part of the telescoped rachis (Fig. 148). 



Whether or not the stipules are recognized as parts of the primitive 

 angiosperm leaf, they show great variety in form and relation to other 

 parts of the leaf. Evolutionary modification is obvious, and there are 

 two very different concepts of the direction of the series. According 

 to one concept, paired stipules, free or partly adnate, represent the 

 primitive leaf structure. With specialization, adnation became complete, 

 with the stipule tips becoming auriculate at the base of the blade. Re- 

 duction and loss of the auricles left a simple sheathing leafbase, con- 

 sisting of the united "leafbase" and the stipules, an apparenUy simple 

 but really complex structure. 



According to the other concept, the primitive angiosperm leaf had a 

 prominent sheathing base and a blade, sometimes separated by a 

 petiole. In specialization, this sheath became auriculate and, with 

 shortening of the sheath, became auricles. Under this concept, free 

 stipules are the higher type; under the other concept, free stipules are 

 the most primitive. Under one theory, the monocotyledons, under the 



