48 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY 



only illustrate what may be observed in nature. A composite with ray 

 florets often has eight only. This was the case with the wild Dahlia and 

 Zinnia, but under cultivation the number rapidly increased. Chrysoccma 

 has regularly five only, thereby mimicking a five-petalled flower. One 

 common by road-sides near Cape Town, and in a semi-starved condition, 

 always bore three ray florets only. A correspondent informs me that in 

 counting the ray florets of a South European marigold the maxima were 

 21 and 34, being correlated with their habitats. Thus 21 is the usual 

 or typical number ; but near the sea the first maximum rose to 26 

 (=2x13) and 34. " The ox-eye daisy has generally 21 florets at the 

 level of Lake Como ; but at a height of 400 to 500 feet on the mountain 

 a form is developed during tlie height oj the flowering season with 34 rays, 

 reverting at the end of the season to 21. The number of ray florets in 

 different composites varies with the environment." 



With regard to the 3 sepals and 8 petals of Ranunculus Ficaria, 

 the former arise from the fact that the plant is monocotyledonous, as stated 

 above, but the change from 3 sepals to 8 petals is due to the fact that the 

 angle of 120° (\) is nearer to 135 (f) than 144° (f), so that the change 

 is easier from the \ to | arrangement than to the ?. 



Conclusion. — I have now endeavoured to give a brief and as clear 

 account as I can of the main facts and principles of Phyllotaxis. But, if 

 we venture to search for a cause of such definite and exact arrangements 

 of leaves, it will probably be fruitless, for as yet no satisfactory explanation 

 has ever been given. It is not enough to say that it is a wise arrange- 

 ment that leaves should not all be over one another, so as to exclude the 

 light and air, and impede one another's functions ; but why are there so 

 many different ways of doing it, as represented by the fractions \, 4, |, &c. ? 



