CH. XI V] SYCAMORE. 185 



large green bunches on the tree. Each key is shaped 

 something like the head of a lance, and consists of a thicker 

 basal part, the cavity of the ovary, and a thinner apical 

 part which serves as a wing, that is to say it serves, like 

 the winged border of the seed sketched in fig. 83, to 

 increase the area of the fruit, and make it fall slowly 

 through the air. It is certainly not a perfect flying 

 mechanism, but it is interesting as a rough approximation 

 to more complete adaptations. The ovary of the ash is 

 built of two carpels so united as to form a pair of cavities 

 in each of which are two ovules. Of these only one 

 comes to maturity, and when the ovary is opened in the 

 manner recommended in the Practical Work, a single 

 seed is found together with three undeveloped ovules. 

 Such a struggle for life among ovules is not uncommon 

 and another instance occurs in the Sycamore. 



Sycamore, Acer pseudoplatanus. 



Those who have lived in the country must be familiar 

 with the winged "seeds" of the Sycamore spinning and 



FIG. 86. 



FLORAL DIAGRAM OF THE SYCAMORE (Acer pseudoplatanus). 

 From Le Maout and Decaisne. 



