ORIGINS OF EMBRYONIC PATTERNS 



647 



perimental conditions may give a pattern very different from that which 

 we call "normal." 



SOME EMBRYONIC PLANT PATTERNS 



Botanists have apparently been less generally concerned than zoolo- 

 gists with questions of the origin and nature of embryonic pattern, but 

 botanical literature contains many interesting and suggestive data and 

 raises various questions concerning pattern. A few of these are briefly 

 noted. 



B 



C 



Fig. 206, A-C. — Embryonic pattern in moss and fern. A, embryo of a moss with part of 

 archegonium in longitudinal section (from Child, 1915c, after a preparation loaned by W. J. G. 

 Land); B, C, diagrammatic, indicating relations of embryonic regions in ferns to archegonium 

 and gametophyte, anterior end of prothallium to the right (after Coulter, Barnes, and Cowles 

 Textbook of Botany, 1910). 



CRYPTOGAMS 



The case of the alga Fuciis and related forms has been discussed in 

 another connection (p. 423). Among the bryophytes the polarity of the 

 embryo is generally coincident with the longitudinal archegonial axis, the 

 apical end being directed toward the neck of the archegonium. Figure 206, 

 A , the embryo of a moss in longitudinal section, shows this axial relation 

 and indicates the presence of an apicobasal gradient in physiological con- 

 dition by the basipetal decrease in depth of staining and increase in size 

 and vacuolation of cells. 



Axial relations of the embryo to the archegonium and to the gameto- 

 phyte differ in different groups of the pteridophytes, suggesting that in 

 some the archegonium may be the factor determining the primary pattern, 



