160 REV. PROF. G. HENSLOW ON THE ORIGIN OF 
Fig. 2. 
4 
1 
In this diagram of a spiral of the 4 divergence, the first cycle contains the numbers 1, 2,3; No. 4, which would 
begin a new cycle, naturally falls over No. 1; but in establishing whorls the “law of alternation ? interferes 
and shifts No. 4 through 60°, as indicated by the arrow. Hence the second cycle now contains 4, 5, 6. 
No. 7 would similarly fall over No. 4, but it is also shifted through 60°, and so on for the Nos. 10, 13, 16, 
and 19, 
The result is a series of single cycles of three members each, giving rise to separate whorls of threes, 4 true 
di-trimerous whorl being impossible. The first two whorls are often quite distinct, as a calyx and corolla, 88 
in Hydrocharis, Alisma, and Tradescantia ; but, of course, more often they are alike, forming the so-called 
perianth. Similarly the two cycles or whorls of three stamens each now form one, what might be called falsely 
acquired, di-trimerous whorl, since the 2 divergence is extremely rare in the foliage of Monocotyledons. 
