564 TRANSACTIONS OF SECTION K. 



2. Many erratic blocks have been purchased. 



3. Especially fine trees have been protected. 



4. A ' National Park ' of about two hundred square kilometres is in course 

 of establishment in the Lower Engadine. Ninety kilometres have already been 

 acquired. 



3. Phytogeography as an Experimental Science. 

 By Professor Jean Massart. 



Each habitat, possesses its own strictly adapted flora. Some species, how- 

 ever, are to be met with in stations which differ markedly from each other. 

 Thus Koeleria cristata occurs both on limestone rocks and on sand dunes : 

 Pelvetia canaliculata on wave-beaten rocks, and in shallow depressions in salt 

 marshes, and Veronica hederozfolia as a weed of cultivation and also in rocky 

 woods. 



Sometimes the forms from these different stations have been given special 

 names, e.g., Matricaria maritima and M. inodora; Polygonum amphibium nutans , 

 terrestre and coenosum (xerophytic). But although they have been separated 

 by systematists, these forms have not in all cases originated by variation. 

 Experiments have proved that some of them are merely the result of plasticity, 

 i.e., the power of organisms to adapt themselves to their surroundings. Thus 

 seeds of Matricaria maritima when sown in a garden, at once give rise to 

 M. inodora; a cutting of Polygonum amphibium natans, planted in wet earth, 

 becomes P. a. terrestre, and in dry earth, P. a. coenosum. Conversely, P. a. 

 terrestre and P. a. coenosum may just as easily be changed to each other or to 

 P. a. natans. But what about Koeleria cristata albescens, Anthyllis V ulneraria 

 maritima, and the numerous varieties of Ranunculus aquatilis ? Experiment 

 alone will decide whether they are true systematic varieties or simply adjust- 

 ments to altered conditions. 



The most interesting of these species are those which have the same 

 characters in various habitats, e.g., Blackstoniu perfoliata looks the same in 

 limestone pastures and in dune valleys. Again, Pteridium aquilinum and 

 Calluna vulgaris are the same on the limestone pavements of West Ireland as 

 on heaths and moors. What makes these calcifuge species able to grow on 

 limestone in Ireland ? Is it because the climate is so extremely favourable that 

 they can withstand the annoyance arising from the calcareous soil ? Or because 

 the limestone plants are biologic races, analogous to the races of some parasitic 

 fungi ? Or because some particular species whose competition is everywhere too 

 strong on limestone do not exist in Ireland ? Direct experiment is the only 

 means of ascertaining whether any of the above explanations be the right one. 



The struggle for life no doubt plays an important part in plant-geography. 

 Recent experiments have shown that plants excrete certain substances into the 

 soil, which are toxic to themselves and especially to others. Fairy rings of 

 fungi are probably manifestations of such soil poisoning. When a patch of 

 ground is manured in the middle of a heath and converted into a meadow, the 

 original heath vegetation is unable to re-colonise the cultivated land. Birch 

 trees are not common constituents of forests in calcareous districts, yet they 

 thrive in clefts of limestone rocks where no other trees contend with them. 

 It is likely that the absence of Calluna, Nardus and Molinia on fertile soil, and 

 of birch trees in calcareous woods are mainly due to concurrence. Experiment 

 on such topics would be most welcome. 



The origin of species by means of hybridisation is another chapter where 

 experiment takes the pre-eminent place. But here the necessity for experiment 

 has been long recognised, and numerous hybrids have already been studied, 

 both themselves and their offspring. Some very interesting hybrids, however. 

 e.g. Cirsium, Betula, and Quercus, have not yet been made. 



The power of accommodation, the struggle for life, the origin of species, and 

 other problems of prime importance for phytogeography are now ripe for 

 experimental study. 



