462 LINNJEAN SUBDIVISIONS; EFFECTS OF CULTIVATION. 



Necessaria. Lastly, there are a few of the Cynarocephalae in 

 which the florets of the disk are perfect ; whilst those around 

 the margin are larger than the rest, so as in some instances to 

 form a sort of ray (being still tubular, however,) and are entirely 

 infertile. These are termed by Linnaeus Frustranea, from their 

 incomplete character. 



632. It is chiefly among the Radiate group of this order, 

 that those species exist, which are valued as garden plants ; and 

 cultivation has frequently a remarkable effect on them. The 

 corolla of the florets situated towards the margin of the disk 

 undergoes an increased development, at the expense of the true 

 reproductive organs ; and they are changed into ligulate florets, 

 deficient in stamens, and exactly resembling those of the ray. 

 This change is particularly evident in the Dahlia, which has 

 repaid the attention it has received, by a greater improvement 

 in the aspect of its flowers, than any other species, perhaps, has 

 exhibited. In its natural condition, it possessed, like most of 

 its group, but a single row of ligulate florets ; and all the centre 

 of the flower was occupied by the ordinary yellow disk. Under 

 the influence of a rich soil, however, the number of rows of ligu- 

 late florets has gradually increased : and these have also under- 

 gone great changes in regard to their size, elegance of form, and 

 beauty and variety of colour. When a Dahlia is spoken of as 

 eight, ten, or twelve-bloomed, it is meant that it has eight, ten, 

 or twelve rows of ligulate florets. In its highest state of excel- 

 lence as a garden flower, the florets of the disk nearly or alto- 

 gether disappear ; and the smaller the eye (as it is termed) of 

 the Dahlia, the better it is considered to be. Such flowers, 

 however, are not fertile, that is, they do not produce ripe seed ; 

 for the conversion of the complete florets into those bearing pistils 

 only, occasions a great deficiency of pollen. It is curious to 

 observe the change which will be produced in the flower of a 

 Dahlia, if a root of the best kind be planted in a poor soil. 

 There will be an effort, so to speak, to produce a large number 

 of ligulate florets ; but these will be stunted and often curiously 

 twisted ; so that the flower is even less handsome and regular 

 than that of a much poorer kind. The Dahlia is a native of 



