386 NATURAL SCIENCE. j UN e, 



2. Innumerable, slight, individual variations — the " develop- 

 mental characters " of Wallace, because they are due to the ever 

 varying growth and development of the plant. They are usually 

 transient, i.e., not hereditary and " non-specific " (Wallace), though 

 they may become true varietal or specific characters under 

 circumstances different from their normal conditions. Thus, e.g., 

 probably no two leaves of Ranunculus Ficavia are absolutely alike in 

 this country, but the variations are insufficient to suggest any varietal 

 differences. In the Mediterranean regions, however, the whole plant 

 bears finer and larger flowers and leaves, so that it is generally 

 recognised as the variety Caltha folia. 



3. Self-adapted varietal characters, which do not exist until 

 called into existence by a pronouncedly different environment. These 

 are the main sources of true varietal and specific characters, and give 

 rise to the well marked " facies " of plants growing in deserts, 

 marshes, water, etc. 



Variations (as of number 2) in the parts of plants of the same 

 species, when growing in the. same place and under the same con- 

 ditions, are very common. Mr. Burkill, for instance, has lately 

 alluded to variations in floral symmetry, which I called " symmetrical 

 reduction." 2 He describes the numbers of stamens and carpels in 

 the flowers of several plants ; thus he says : — " Ranunculus Ficavia 

 showed that towards the end of the flowering period both the stamens 

 and carpels become reduced in number without their proportion being 

 changed." 3 He regards temperature as a cause. I have had more 

 than one occasion to allude to this feature of "reduction," as well as 

 of " symmetrical increase." 4 The former is sometimes attributable 

 to a barren soil (tetramerous flowers of Potentilla Tormentilla), or to a 

 feeble vitality (early flowering trimerous Fuchsias), or an acci- 

 dental and locally insufficient supply of nutriment (tetramerous 

 flowers in a corymb of elder, etc., in pentamerous instead of hexa- 

 merous flowers of Lythvum Salicavia, and in dimerous flowers of iris, 

 orchids, etc.) On the other hand, symmetrical increase is due to 

 hypertrophy ; as in a large tetramerous crocus now before me, in 

 heptamerous, central flowers of a glomerule of Lythvum Salicavia, and 

 in the polymerous flowers of cultivated auriculas, etc. 



Symmetrical increase is, of course, quite a different thing from 

 "doubling"; as this latter is due to the conversion of stamens and 

 carpels into petals, coupled with their multiplication. 



I would here observe, that a reduction as well as an increase of 

 the symmetry may be transient, as in all the preceding plants men- 

 tioned, except the Tormentil, in which the quaternary flowers have 

 now assumed a truly specific character. Similarly, speaking 



2 Note on the " Causes of Numerical Increase of Parts of Plants," Joum. Linn. 

 Soc, 1877 ; " Origin of Floral Structures," p. 18, etc., 1888. 



8 Nature, Feb. 7, p. 359, 1895. 



4 The reader may be referred to my paper on " Self- Fertilisation " (1877), and 

 that on "/Estivations" (1876) in the Trans Linn. Soc. 



