36 



As eacli leaf gets older the folds of green tissue are flattened 

 out. the leaf is thrown outward and downward and the lamina 

 is expanded more or less horizontally, with the upper surface 

 directly exposed to the sun's rays. See Figs. 7 9, Plate IX. 

 Homologous 34. Several cases of the so- 



and Analo- ca }i ef i metamorphosis of plant members have been incidentally 

 Members. mentioned in this and the previous chapters from which it will 

 be seen that members which are alike in their mode and place 

 of origin and general plan of structure are regarded as 

 morphologically the same, however different they may super- 

 ficially appear to be in their form, or function. Members 

 which are thus of the same morphological value are said to 

 be homologous, whereas those members which, although alike 

 in some respects, are not morphologically the same, such 

 as the spines of Berberis and Bel, are called analogous. 



