56 



MORPHOLOGY OF AXGIOSPERMS 



integument so completely coalesces with the nucellus and closes 

 the micropvle that the ovule resembles a naked nucellus. Zin- 

 ger 43 observed that the massive inner integument in Canna- 

 bineae is completely coalescent with the thick outer one over the 

 apex of the nucellus, and the micropylar canal becomes entirely 

 closed by the development of tissue. In cases of chalazogamy 

 and persistent parthenogenesis such behavior of the integu- 

 ments may be expected, as well as in other cases whose habits 

 do not suggest it. 



In most cases, the ovule does not merely become distinct 

 from the surface of the member that produces it, but is borne 

 upon a stalk-like base or funiculus. It is generally stated that 



n ~\-\\- 



Fig. 22. — Forms of ovules (diagrammatic). A, orthotropous ; B, anatropous ; C, cam- 

 py lotropous ; m, micropvle ; e, embryo-sac ; «, nucellus; c, chalaza;/, funiculus. — 

 After Prantl in Engler and Prantl's Nat. Pflanzenfam. 



the ovules of Gramineae have no funiculus, but it would be im- 

 possible to draw an exact line between its presence and absence. 

 The direction of growth of the ovule seems to be related 

 to the orientation of the micropvle in reference to the pollen- 

 tube. Mirbel gave to the resulting forms the names ortho- 

 tropous, campylotropous, and anatropous (Fig. 22). In the 

 first case the growth continues without the development of any 

 curvature, a fact generally true of terminal cauline ovules. 

 Orthotropous ovules are quite common, being found among 

 Monocotyledons in the Restiaceae, Eriocaulaceae, Xyridaceae, 

 certain Araceae, Commelinaceae, etc. ; and among Dicotyledons 

 in the Piperaeeae, Urticaceae, Polvgonaceae, Oistaceae. etc. 

 These are relatively primitive families of Monocotyledons and 

 Archichlamydeae, and confirm the natural impression that the 



