86 THE AMERICAN BOTANIST. 



leaflets droop. The explanation for this seems to be a physio- 

 logical one. In the oxalis the stomata, or openings through the 

 epidermis, are mostly on the under surface, and the drooping 

 position of the leaflets protects them through the night. The 

 stomata of marsilia, on the other hand, are mostly on the upper 

 surface, and the leaflets naturally bring their upper surfaces 

 together in the night position. — Fern BiiUctin. 



Plant Distribution. — It is often a narrow line that 

 prevents some cultivated plants from becoming weeds. If 

 petunia, tomatoes, pumpkins and other food-plants of tropical 

 origin could survive our winters we might soon find it neces- 

 sary to hoe them out of spots in the garden where they were 

 not wanted. These plants, however, cannot usually get 

 through our winter even in the seed. An illustration of what 

 might happen if they could is found in an insignificant Mexican 

 weed, Galinsoga parviflora, that has slowly invaded the Unit- 

 ed States. The mature plants cannot endure our winters, 

 but the seeds can and as a consequence the plant is steadily 

 increasing its territory. Doubtless there are other plants of 

 this character, the jewel-weeds (Impatiens) for instance. 



Pollination in Evening Primrose. — It will probably 

 take several generations of botanist gardeners to correctly in- 

 terpret even half of the peculiarities possessed by plants. Dar- 

 win's theory of evolution by slow gradations made it neces- 

 sary to account for every thorn and prickle, every shape and 

 turn of a leaf and all color, and as a consequence the litera- 

 ture of botany since Darwin's time has been full of explana- 

 tions that in the light of our present knowledge do not explain. 

 The thorns of the hawthorn do not appear to be necessary 

 to the presentation of the species, nor does any significance ap- 

 pear to attach to the color of the juice of the poppy-worts. 

 The foregoing has been suggested by an observation of De 



