570 



THE POPULAR SCIENCE MONTHLY 



cessions of gypsum and repeated heavy dews 

 the accumulatiou of plaster goes on increas- 

 ing, the cracks are enlarged, and in time the 

 stone is split. 



Variations in the Forms of Water-PIants. 



Dr. W. Bchrens, of Brunswick, has pub- 

 lished a preliminary report of researches 

 which he has been making into the influence 

 of the movement, and other physical rela- 

 tions, of water upon the plants growing in 

 it. He observes that water-plants, both 

 those that grow submerged and those which 

 appear on the surface, are subject to a va- 

 riety of modifications in the forms of their 

 stems, leaves, and other organs, according 

 as the water in which they grow is in more 

 or less lively motion. Plants which grow in 

 a stream, and are rooted in the ground, 

 seem to receive a kind of pull from the 

 moving force of the water, which is propor- 

 tioned to the speed of the current. If plants 

 which grow indifferently in standing, mod- 

 erately moving, and swift waters, exhibit 

 variations which are constant for the same 

 kind of waters, the conclusion is allowable 

 that the variations are produced by the ki- 

 netic influence of the waters. Plants which 

 are met in only one kind of waters do not 

 exhibit equivalent variations. The common 

 frogbit, of Europe, which floats on the sur- 

 face of still waters, has its leaves always 

 of the same broad kidney-form. The pond- 

 weed, which grows both in still and rnnning 

 waters, exhibits, on the other hand, mani- 

 fold variations. The most common form 

 has floating, oval leaves, the diameters of 

 which are to each other as 1 to Vo. The 

 leaves of those varieties that grow in run- 

 ning water are longer and narrower in pro- 

 portion to the swiftness of the stream ; and 

 one form is mentioned in which the diame- 

 ters of the leaves are as 1 to 3. The wa- 

 ter-ranunculuses (Batrachium) afford excel- 

 lent examples of the influence of running 

 water on the forms of plants. Several spe- 

 cies are found in all kinds of waters, the 

 most of them having leaves of two forms, 

 peltate floating leaves, and much divided 

 submerged leaves. They grow in still and 

 running, fresh and brackish waters, and 

 even on the land after the water has dried 

 away. Of the species common in Europe, 

 Batrachium aquatile is the most interesting 



object of study in respect to its variations. 

 Its forms are numerous, but they may be ar- 

 ranged under two general heads. The first 

 includes those varieties which have plain 

 floating leaves and also divided, submerged 

 leaves, and the second those which have 

 only divided leaves under water. The forms 

 of the former class occur principally in 

 waters having little motion; the floating 

 leaves are round and peltate, with fine slight 

 scallops on the borders. In swifter waters 

 the leaves are cut up into pointed lobes, 

 the distinctness of which increases with the 

 speed of the current. Dr. Behrens has dis- 

 tinguished about thirty varieties in different 

 waters, most of which he has described and 

 named in his paper. In the swiftest cur- 

 rents, the floating leaves disappear, and only 

 the varieties of the second form those hav- 

 ing exclusively divided, submerged leaves 

 are found. Still another change comes over 

 the Batrachium when the water is taken 

 away from it. It grows up with a short 

 stem, and is thickly covered with gceen 

 leaves divided into numerous short, firm, 

 succulent lobes. Dr. Behrens is preparing 

 a work in which variations of this sort will 

 be fully discussed, with illustrations. 



Progress in Photograpliv. " Some Re- 

 cent Advances in Photography " is the sub- 

 ject of a paper recently read before the 

 Society of Arts by Captain Abney, R. E., 

 F. R. S., in which reference was made to 

 the more important improvements in the 

 art that have been put in practice since 

 1875. A new negative process, called the 

 gelatino-bromide process, offers decided ad- 

 vantages. It consists in the use of a 

 gelatine emulsion of silver bromide for the 

 sensitive surface. With a plate thus pre- 

 pared, a photograph may now be taken in 

 one second of time which it formerly took 

 thirty seconds to secure ; and a plate can be 

 prepared which needs an exposure of only 

 one sixtieth of a second, when a view is 

 fairly lighted to secure a soft and harmoni- 

 ous negative. It makes instantaneous views 

 possible under cii'cumstances which were im- 

 possible, in illustration of which the speaker 

 exhibited a view in which the shadow and 

 reflection of a swallow passing in the air 

 over a pond were perfectly represented. 

 The plates and the development of pictures 



