File:Botany for high schools (1910) (20379604016).jpg

Title: Botany for high schools
Identifier: botanyforhighsch00atki (find matches)
Year: 1910 (1910s)
Authors: Atkinson, George Francis, 1854-1918
Subjects: Botany
Publisher: New York, H. Holt and Company
Contributing Library: Wellesley College Library
Digitizing Sponsor: Boston Library Consortium Member Libraries

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
LEAVES, THEIR FORM AND MOVEMENT 81 136. Relation of leaves to light.—This is preeminently a subject for field or outdoor study. Observations show that leaves assume the most advantageous arrangement and position to receive the best lighting. In many cases, when the leaf arrangement on the stem may be three, five or eight ranked, the leaf blades may be all arranged in a single plane, to receive the light from one direction. This often occurs in woods or groves, the petioles of the leaves twisting so as to allow the blade the most favorable position. Mosaics or patterns are formed where a number of leaves on a single shoot lie so that they are fitted in almost like pieces of mosaic and so that there is very little shading of adjacent leaves. Fit- tonia grown in greenhouses is a splendid example. Rosettes are formed when the leaves are crowded on the stem near the ground in the form of a rosette. Imbricate patterns are seen where the leaves are not so closely crowded, but overlap something like shingles on a roof so that light can reach the leaves. In the radiate pattern the leaves radiate in all directions from horizontal to the vertical and thus obtain a good light relation, as in the screw pine (Pandanus) often grown as an ornamental plant. 137. Irritability of ten- drils and twining stems.— When a tendril or a twining stem, as it slowly sw^ings around, comes in touch or contact with some object, this contact stimulus causes it to bend at this point bringing new^ points in contact so that
Text Appearing After Image:
Fig. 71- Leaf of Venus fly- trap (Dionaea musci- the tendril or stem then coils p^/.^)' showing winged petiole and toothed around the object of support. Fig. 72 Leaf of Drosera ro- tundifolia, some of the glandular hairs folding inward as a result of a stimulus. 138. Response of insectivorous plants to touch.—Remark- able movements are shown by the leaves of some insectivorous plants. In the Venus's flytrap (fig. 71) the terminal part of the leaf is shaped like a steel trap. The blade is broad and the margin rounded and beset with numerous hairs or spines resembling the

Note About Images