PART III. | THE MECHANISMS OF FLOWERS. 423 
mature stigma, The drooping flowers of Borago, and the position 
of their anthers, exclude all insects which cannot hang, as bees 
can, below the flower and insert their proboscides into the narrow 
opening. Symphytum and Cerinthe, finally, besides offering the 
same difficulties as Borago, have a tube which requires so long a 
proboscis to reach its base, that only humble-bees and other bees 
with a proboscis equally long can reach the honey. 
Orv. CONVOLVULACE ZZ. 
311. CONVOLVULUS ARVENSIS, L.—Sprengel has described the 
chief characters of this flower very clearly, contrasting them with 
those of C. sepiwm. 
The funnel-shaped corolla is yellow at the base internally, 
elsewhere either white or red, and marked in the latter case with 
Fic. 143.—Convolvulus arvensis, L. 
1.—Transverse section, through the base of the flower (x 7). 
2.—Essential organs, from an expanded flower (x 33). 
a, style; b, filament; ¢, entrance to nectary; d, corolla; e, calyx. 
five radiating white streaks. These “pathfinders,’ and the habit 
of closing, both in the evening and in rainy weather, mark out the 
flower as adapted for the visits of diurnal insects. The orange-red 
under surface of the ovary secretes honey, which is lodged in the 
lowest, narrowest part of the corolla, and sheltered by tbe broad 
bases of the stamens, which leave five narrow openings leading to 
it. The stamens arising thus with broad bases from the corolla, 
adhere to it for a short distance, and then curve inwards, coming 
close together around the style; the filaments, where they are in 
contact with one another, are closely beset with small, stiff pro- 
jections, which prevent an insect from thrusting its proboscis 
