IRISH GARDENING 



VOLUME XV 

 No. 167 



Editor-J- W. Besant 



A MONTHLY JOURNAL DEVOTED TO THE 



ADVANCEMENT OF HORTICULTURE AND 



ARBORICULTURE IN IRELAND 



JANUARY 

 1920 



Variety of Plant-Form in some Familiar Genera* 



By II. Lloyd Pkaegkr, B.A.B.E. 



O the horticulturist for 

 whom the differences of 

 form which plants dis- 

 play is a matter which 

 comes daily under his 

 notice, and lies, indeed, 

 at the very foundation 

 of his art, any ordered 

 thought on variation in 

 plants ought to be of 

 interest. On this plea 

 I set down a few notes on difference of 

 form as found within some familiar genera. 

 A genus we may define in a rough and 

 ready way as a number of different kinds 

 of plants (what we call ■species), whi;-h 

 nevertheless possess such similarit}' of appear- 

 ance and structure (especially of the powers 

 ^hich, from all points of view, are the mos> 

 important part of plants) that they suggest a 

 common ancestry. To take the case of a genus 

 in which the species, though numerous, have 

 not departed far from the presiunable ancestral 

 type, consider the roses. Though they have 

 split into a large number of species, and have 

 dispersed themselves over the whole northern 

 hemisphere, they have maintained a strong* 

 family likeness. All are shrubs, all have pin- 

 nate leaves, all have the same type of flowers 

 and fruit. We can easily envisage a common 

 parent for them all. When and where did that 

 parent live ".' That kind of question can seldom 

 be answered, and its consideration would lead 

 us quite out of our depth, and into difficult 

 byways of geology and palaeontology. Suffice 

 it to say that remains of roses have been found- 

 in deposits of the Great Ice Age — laid down 

 possibly a lumdred thousand years ago— and 

 the genus probably arose, like many which now' 

 inhabit the earth, in the period which geologists 

 call Pliocene, the age of which it is impossible- 

 to express in years, but w-hich is separated from 

 the present by an interval at least twice at? 

 great as the huge figure already mentioned. All 



our plants have had a very long time in which 

 to spread and have special character stamped 

 upon them. How do they acquire new 

 cliaracters? Another profound question, im- 

 possible of direct answer, and impossible to dis- 

 cuss in the limits of a popular article. But jt 

 may be broadly admitted that, granting a ten- 

 dency to vary, a study of plants as they grow 

 will soon convince the enquirer that, at lertst 

 A\ithin the limits of a genus, many of the more 

 striking characters by which one species is dis- 

 tinguished from another are due to the influence 

 of the environment — to the klna of situation in 

 which they have chosen to grow. To illustrate 

 this, let us take another ■ common, genus. 

 Ranunculus, or Buttercup. Here agam ■ we 

 find in general no very wide divergence from 

 a common type ; but a number of the species, 

 forsaking the meadows or marshes which form 

 the home of tlie majority, have taken to the 

 water, and lead an aquatic life. These have quite 

 altered their mode of growth, and have 

 mimicked in important respects the ancient 

 denizens of lakes and seas. The stems have 

 become elongated (sometimes to a couple oi* 

 yards), slender and llexible, the leaves if sub- 

 merged divided into hair-like segments, or, if 

 floating, undivided, smooth, and tougb. All 

 these features are characteristic of water 

 plants, and are designed to render them secure 

 under stress of wave action. It seems clea' 

 that these species,, coming from a marsh-loving 

 ancestry, and the genus still shows a predilec- 

 tion for a damp; habitat, have advanced into the' 

 water and in self-defence have taken on the 

 special characters which make' water-life toler- 

 able. 



The genus Veronica will furnish an interest-, 

 ing case of a different kind. This is a very large 

 group widely spread over the earth's surface. 

 W^hile most of the species are herbs, often of, 

 small size,' the New Zealand Veronicas have 

 taken on an arboreal habitat — it is impossible, 

 to say why— and now form a large group oi 



