1888.] NATURAL SCIENCES OF PHILADELPHIA. 391 



CONTKIBTJTIONS TO THE LIFE HISTORIES OF PLANTS. No. III. 

 BY THOMAS MEEHAN. 



Smilacina bifolia. Observing in a large tract of Smilacina bifolia 

 that the leaves were for the most part at a very light angle, indeed 

 almost vertical, it seemed to afford a good opportunity to test a 

 prevalent idea that, in such cases, the stomata are nearly equal in 

 numbers on each surface of the leaf. Dr. J. B. Brinton kindly made 

 a careful microscopical examination of some leaves I furnished him 

 with, but he found no difference in this respect to leaves with a 

 purely horizontal direction. On a small section, of which he hands 

 me a drawing, there was only one stoma on the upper surface, 

 while there were fifteen on the under surface. 



Dichogamy and its significance. Dichogamy has reference to the 

 relative period of maturity of stamen and pistil. When the stamens 

 are in the advance the flowers nre said to be proterandrous ; when the 

 pistil is mature before the stamens, the flower is proterogynous. Usu- 

 ally the term is employed in connection with hermaphrodite flowers. 

 But as it is a mere question of the time required for the development of 

 the sexual organs necessary to the perfecting of a complete individual, 

 it is obvious that we may extend the term so as to include monoecious 

 and dioecious plants. 



The law under which the separate sexual organs are retarded in 

 their growth in some instances and accelerated in others, cannot 

 but have supreme importance in the study of vegetable biology. If 

 we can trace the working of this law in the hermaphrodite flower to 

 the extent of acceleration or retardation for but a single day, we can 

 easily get to understand how some plants may come to have the 

 maturity of these organs days apart, and to finally divide into 

 monoecious or dioecious classes. 



Among the contributions I have made to botanical science, few 

 impress me with more importance than the determination of the fact 

 that a degree or measure of heat capable of exciting the male organs 

 to growth, may yet be wholly inadequate to start growth in the 

 female (see Proceedings of the Academy of Natural Sciences 1885, p. 

 1.17.) 



I observed that the aments of walnuts, hazel-nuts and similar 

 plants were often perfected weeks and occasionally months before 

 the female flowers were in conditon to receive pollen, and that it 



