June 18, 1897.] 



SCIENCE. 



937 



the varieties aquaticuni and terrestre of some 

 manuals. From F. Hildebrands simple but 

 pretty experiments* we know that plants 

 of the latter variety which have grown for 

 years in dr}' places will, when submerged 

 a few feet in water, produce shoots that 

 bear in a few weeks the typical floating 

 leaves. While stomata are disposed chiefly 

 over the lower surface of the leaf in the 

 land form, in the aquatic they exist on the 

 upper surface. 



Experiments with Sagittaria, Eidiornia, 

 Potamogeton and others would demonstrate 

 that in all there is an extreme plasticity of 

 form that permits environmental adap- 

 tibility. Comparison with all the species of 

 each genus causes us to inquire whether 

 one of the variation forms has not been ac- 

 quired through response to stimuli, and has 

 now become a hereditary condition ? We 

 need not now stay to answer. 



(2) Shore, littoral or halogen plants. Abun- 

 dant along the eastern seaboard is the 

 crimson-flowered Gerardia purpurea, that is 

 as variable in habit as it is in the selection 

 of its situation. AVithin a distance of 100 

 yards, it may be gathered on a dry exposed 

 sandy bank, and be then about 12 inches 

 high, sparcely branched, faintly red in the 

 leaves, and pale pink in the flowers; or on a 

 flat shady spot in richer soil, when the stem 

 may be 2 feet high, the leaves bright green 

 and elongate, and the flowers pink crimson; 

 or on a rich alluvial mud, when we get a 

 bushy plant 3 feet or more high, that bears 

 long narrow leaves and large showy crim- 

 son flowers. But in our botanical manuals 

 G. maritima is now given as a true species. 

 It inhabits saline coast-flats, and may even 

 be washed by sea-water without seeming to 

 be injured. A distinctly different plant it 

 looks from the former. From 1 to 8 inches 

 high, it branches little if at all, bears thick 

 succulent reddish-green or glaucous leaves, 

 and one or several small pink flowers. 



*Bot. Zeitung, 1870. ' 



On nearly every coast the two can be 

 gathered in close proximity. At Oyster 

 Bay the Shore Railroad separates a drained 

 shore-flat with abundance of G. purpurea 

 from an undrained saline swamp that is 

 filled with G. maritima, while near Vineyard 

 Haven a drain ditch forms the line of de- 

 marcation between the two. Microscopic 

 study of both causes one to ask whether 

 they deserve to be regarded as distinct 

 species. The answer to this may depend 

 wholly on what we call a species, but study 

 of a finely graded set, gathered fully four 

 years ago at Sea Isle, on an inclined bank, 

 would lead me to regard them as common 

 forms that environment has altered. If 

 this be so we should expect that within a 

 longer or shorter period a single individual 

 in its life time, or seminal descendants of 

 such as are gradually ' acclimatized,' will 

 develop macro- and miero-scopic characters 

 similar to those of Gerardia maritima. The 

 studies of Lesage* and Eussell,t amongst 

 others, yield definite proof. Both have 

 compared, microscopically, individuals of 

 certain species from littoral and inland 

 regions, and the changes undergone by the 

 shore-grown individuals exactly correspond 

 with those exhibited by Gerardia maritima. 



Increase in thickness of the leaf sub- 

 stance chiefly through increase in, and en- 

 largement of, the pallisade cells; an appar- 

 ent reduction, or possibly wider dispersion, 

 of the chloroplasts; greater lignification of 

 the stem and leaf-bundle elements; enlarge- 

 ment of the vessels; reduction in size of the 

 intercellular spaces, are typical phenomena. 

 The culture experiments of Lesage further 

 verify his field observations. Russell frankly 

 confesses that those grown by him in saline 

 solutions were not so vigorous as those from 

 the Paris basin. Even in this, however, 

 the resemblance to our plant is perfect. 



But as Gaston Bonnier has well empha- 



* Eev. Gen. de Botanique, Vol. 2, 1890. 

 tAnn. Sc. Nat. (Bot), 1895. 



