SCIENCE-GOSSIP. 



STATIONS OF PLANTS AND BUOYANCY OF SEEDS. 



By H. B. Guppy, M.B. 

 {Concluded from page 43.) 



*"pHE groups, of which some typical examples are 

 given below, afford very significant indications, 

 and we are thus enabled to advance another stage 

 in our line of reasoning. Nature has, so far, taken 

 advantage of the floating capacities of dry inde- 

 hiscent fruits that she has located most of the plants 

 in question at the river's side or at the pond's edge. 

 Since it has been already shown that nearly all 

 the plants that exhibited considerable floating 

 powers in their fruits or seeds possessed fruits of 

 this character, it would seem that there are gathered 

 at the margins of rivers and ponds most of the 

 British inland plants that could be assisted in their 

 distribution by the agency of water. 



The great sifting experiment has been a work of 

 the ages, and we here get a glimpse at nature in the 

 act of selecting a station. But the curious 

 character of the sorting process becomes yet more 

 evident when we find that the buoyancy of the fruits 

 of different species of the same genus and of different 

 genera of the same family may become a matter of 

 station. Of three species of Stachys which have 

 been experimented on, viz., S. betonica, sylvatica 

 and palustris, the last alone possesses buoyant 

 fruits. The fruits of Galium palustre float well, 

 whilst those of G. aparine and of other species of 

 the same genus display but little buoyancy. The 

 achenes of Potentilla comarum float indefinitely, and 

 in their integuments M. Kolpin Ravn has found 

 the " tissu aerifere" of buoyant fruits. On the 

 other hand, those of P. tormentilla have little or no 

 floating powers. Of the following labiate plants, 

 Salvia verbenaca, * Lycopus europcens, * Mentha 

 aquatica, Thymus sp., Calamintha officinatis, Nepeta 

 glechoma, N. cataria, Prunella vulgaris, * Scutellaria 

 galericulata, Stachys betonica, S. sylvatica, * S. 

 palustris, Ballota nigra, Lamium purpureum , L. album, 

 Teucrium scorodonia, and Ajuga reptans, only the four 

 species preceded by asterisks have fruits that can 

 float a long time ; in all the other species the fruits 

 sink at once or in a few days. Amongst the com- 

 posite plants below named, the two species of 

 Bidens alone exhibit any buoyancy worth speaking 

 of ; their fruits often float for indefinite periods, and 

 those of B. tripartita are provided with a covering 

 layer of the "tissu aerifere." The species are 

 Aster tripolium, Bidens cemua, B. tripartita, Chrysan- 

 themum leucanthemum, C. segetum, Matricaria inodora, 

 M. chamomilla, Achillea millefolium, Tussilago farfara 

 (Darwin), Senecio vulgaris, S. aquatints, S. palustris 

 (Ravn), Carduus nutans (Thuret), C. lanceolatus, C. 

 palustris (Ravn), C. arvensis, Tragopogon pratensis, 

 T. porrifolius (Thuret), Helminthia echioides, Leontodon 



autumnalis, Sonchus oleraceus (Thuret and Guppy), 

 Taraxacum dens leonis, Crepis virens, Crepis sp., and 

 Lapsana communis. Amongst the Umbellifera, the 

 following species exhibit in their fruits considerable 

 floating powers, viz. : Hydrocotyle vulgaris, Cicuta 

 virosa (Ravn), Slum latifolium (Ravn), S. angustifolium 

 (Ravn), CEnanthe crocata, Angelica sylvestris, and 

 Peucedanum palustre (Ravn). On the other hand, 

 the fruits of JEthusa cynapium, Pastinaca sativa, 

 Chcerophyllum sylvestre, C. sativum (Thuret), and 

 Smyrnium olusatrum display but little buoyancy. 

 The fruits of Apium nodiflorum and A . inundatum do 

 not conform to the principle illustrated by the 

 other twelve species and soon sink in water. (In 

 the instances where I have made use of the obser- 

 vations of others, the name of the observer is given 

 in brackets.) 



My object here has not been to label facts but to 

 record indications ; and it will be gathered from the 

 foregoing remarks that this is eminently a subject 

 for investigation. We desire, for instance, to know 

 why the yellow iris and the alder frequent the river- 

 side. The iris seeds and the alder fruits, are able 

 in most cases to float for a long time, and it is 

 suggested that those of their congeners away from 

 the river soon sink. At all events, as recorded by 

 M. Thuret, the seeds of Iris chamceiris and /. ungui- 

 cularis possess no buoyancy. We may also ask 

 whether, except in the case of littoral species, 

 buoyancy in a fruit or seed has been a factor of 

 much importance in the geographical distribution 

 of plants. May it not be that in the station at the 

 river's edge of most of our plants with buoyant 

 fruits we have, to quote from a letter of M. Kolpin 

 Ravn, " le plus grand effet de l'adaptation a la 

 dissemination par l'eau." 



As a postcript to this page I may mention with 

 regard to the three British species of Convolvus, 

 that the seeds of C. arvensis, whether fresh or dried, 

 for months sink in fresh and sea-water. Of the 

 fresh seeds of C. septum and C. soldanella quite fifty 

 per cent, float after six months in both waters. 

 Further experiment with C. sepium showed that 

 about half of the seeds floated after nine months in 

 sea-water, and thirty per cent, after eighteen 

 months in fresh water. For the results relating to 

 C. soldanella I am entirely endebted to the courtesy 

 of Mr. F. W. Millett, who conducted his experi- 

 ments at Marazion. These matters will be con- 

 sidered more in detail when discussing the effect of 

 buoyancy on the stations and distribution of the 

 Convolvulacese generally. 



6, Fairfield West, Kingston-on-Thames ; February, 1895. 



