338 



MORPHOLOGY OF THE ANGIOSPERMS 



A median part of the cotyledon, with its appendages, has become distal 

 in the germinating embryo. In this high specialization, the sheath has 

 become elongated — even an intercalary meristem has been reported for 

 some taxa — and the stipular cap elaborated in form and tissue struc- 

 ture as a protective, "soil-penetrating" structure. (Protection of buds by 

 stipules is well known in dicotyledons also, as in Liriodendron.) 



Fig. 131. Sketches of seedlings and cotyledons, showing neck of cotyledon free in 

 C, D, and connate with cotyledonary sheath for various distances in the others. 

 A, B, Canna indica; C, D, Asphodelus Ititcus; E, F, Commelina coelestis; G, H, 

 Iris pseudacorus. cs, cotyledonary sheath; h, hypocotyl; l, I", first two leaves; s, 

 seed coat; sc, scutellum. (After Schlickum.) 



The terms ligule and ligular sheath have been rather loosely used in 

 descriptions of monocotyledonous embryos. Though the ligule of the 

 embryo is undoubtedly homologous with the ligule of monocotyledon 

 leaves, these terms obscure the underlying stipular nature of the struc- 

 ture. ("Ligules" are probably not always stipular in nature.) The term 

 stipular — morphologically a better one — should supplant ligular, al- 

 though ligular has been long established. 



