


86 FLOWERING PLANTS 
a single day or night the pollen grains are especially big, in 
order to give more chance of their remaining firmly on the 
stigma. As regards shape, pollen grains are generally ellip- 
soidal; the next most common form is the crystalline, or 
angular ; they may be cubical, etc. (Figs. 54-56). 
The unevenness of the wall and its delicate markings may 
be observed in the pollen grains of almost any plant vate. has 
dry, dust-like pollen. 
Lastly, the delicate contrivances of many flowers for the 
protection of their pollen from wet should be noticed. It 
would be interesting to make a series of observations on this 
adaptation to surroundings. Many flowers, for instance, hang 
down during the rain and spread themselves out in the sun- 
shine ; in some cases pollen is concealed in tubular flowers, 
and thus protected. 
In conclusion, it should be noticed that the adaptations of 
structure to habitat are not so marked in the flower as they 
are in the vegetative organs, the root, stem, and, above all, 
the leaf. 
BIBLIOGRAPHY ON HISTOLOGY. 
‘Elements of Botany” (Cambridge Natural Science Manuals) : 
F, Darwin. 
“*Student’s Text-Book of Botany”: 8. H. Vines, 
“Practical Botany for Beginners”: R. W. Bower and D. T. G. 
Vaughan. 

