. The origin of floral structures : through insect and other agencies. Plants; Flowers; Flowers. 18 THE STRUCTURE OF FLOWERS. would, â with the addition of one more sepal, asstune those represented by Exactly the same procedure occurs in the change from opposite to alternate arrangements of leaves ia the Jeru- salem Artichoke, as I have explained in treating of the varieties of leaf-arrangement in that plant. Galycanthus is another instance illustrating an abrupt change from an opposite condition of the leaves to the ^\ type in the bracts enveloping the flowers, and which then
. The origin of floral structures : through insect and other agencies. Plants; Flowers; Flowers. 18 THE STRUCTURE OF FLOWERS. would, â with the addition of one more sepal, asstune those represented by Exactly the same procedure occurs in the change from opposite to alternate arrangements of leaves ia the Jeru- salem Artichoke, as I have explained in treating of the varieties of leaf-arrangement in that plant. Galycanthus is another instance illustrating an abrupt change from an opposite condition of the leaves to the ^\ type in the bracts enveloping the flowers, and which then pass insensibly into sepals and petals. Symmetrical Increase and Deceease in Plokal Whorls.â As another instance of variability adding further complica- tions, it may be observed that in both kinds of arrangements, namely, of those plants possessing alternate and those pos- sessing opposite leaves, there are many genera-whose floral symmetry ranges from one to some higher number in the different species of the same genus. Thus 4-5-merous flowers are especially common. I found it so in more than 100 genera of 23 oi'ders examined among alternate-leaved plants; and 58 genera of 19 orders among those with opposite leaves. Again, some genera have species the whorls of whose flowers range from 3 to 6 or 6, or from 4 to 6 in the number of parts; others from .5 to 7 or 5 to 8, etc. In these cases it is often quite impossible to explain what has been the immediate causes producing such variations. The only interpretation that can be given is that the primary sym- metry having been originally determined by phyllotazis, it. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Henslow, George, 1835-1925. New York : Appleton
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