THE REV. б. HENSLOW ON THE ORIGIN OF FLORAL JESTIVATIONS. 187 
between the 2nd and 4th; but in no instance amongst the diagrams given does it pass 
beyond two sepals. Lastly, in 7 instances, as stated above, the spiral of the corolla was 
completely reversed in direction from that of the calyx. 
Similarly in turning to Monocotyledons we find, of the two whorls of the perianth, that 
some genera have both revolving the same way, others have one whorl the reverse of the 
other. Moreover the point where the second whorl begins in either case is as variable 
as in Dicotyledons. Thus, of those genera where both whorls revolve in the same 
direction, Pinanga, p. 812, and Commelyna, p. 568, commence the inner whorl with their 
156 part between the 2nd and 3rd leaves of the outer whorl, both being right-handed 
spirals. In Juncus, p. 864, Phormium, p. 844, Lapageria, p. 856, and Alisma, p. 800— 
all being left-handed spirals—the Ist leaf of the inner whorl lies between the 1st and 
2nd of the outer. 
Again, in Colchicum, p. 850, Fritillaria, p. 843, while both whorls revolve to the 
right, the inner commences with its 1st leaf between the 3rd and the 1st of the outer. 
In Butomus, р. 798, Snowflake, p. 786, and Toffieldia, p. 851, the inner whorl com- 
mences diametrically opposite to the last leaf of the outer (that is, it lies between the 
15$ and 2nd leaf of that whorl), and moreover is in these three reversed in its spirai 
direction. In Asparagus, p. 859, the 1st leaf of the inner whorl lies between the 2nd 
and 3rd ; while, lastly, in Tradescantia, p. 868, and the Pineapple, p. 766, it lies between 
the 1st and 3rd. 
These statements clearly show that there is no single law causing a similarity of order 
in every case. On the contrary, the two whorls seem most capriciously arranged, the 
only common character being that in all flowers of two whorls to their perianth these 
should have their members alternating in position. 
The preceding having been deduced from the diagrams of genera, Т examined several 
species, and found that such variations as are here represented in different genera could 
be all illustrated by the flowers of a single species, as of the Snowdrop, Crocus, &е. I, 
however, retain the above paragraphs as referring to the diagrams, which will therefore 
furnish the reader with abundant illustrations. 
УП. On THE CAUSES WHICH DETERMINE THE VARIOUS KINDS OF /ÉSTIVATION. 
l. Regular flowers.—If the parts of a whorl are all on the same plane, it appears to 
be quite uncertain as to which member of the whorl sball be developed as the first or 
outermost, and that, if a calyx or corolla be both quincuncial, although theoretically 
their members are spirally arranged, yet practically No. 1 of the corolla may be any one 
of the five petals, and by no means necessarily as near to 144° as possible from the fifth 
sepal. This may be due to the fact that as the internodes are suppressed the nourish- 
ment is not only equally distributed over the circumference of the receptacle, but nearly 
or quite as equally in time, so that it is, so to say, а mere chance Which part of a whorl 
gets the first start. Some slight differential impulse seems to occur with the first five 
kinds of zestivation; but with the convolute, valvate, and open no member сап be called 
the first at all. i | 
Аз in a single whorl the order of development of its parts is not always in accordance 
with the theoretically spiral arrangement, and still less is there any connexion between the 
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