January, 1907.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



IS 



method of starting from a single seed obviates the diffi- 

 culties stated above. 



This old-fashioned elimination process of plant breeding 

 has been always considered as the most valuable argument 

 in favour of natural selection ; in fact, of late, it was its last 

 remaining botanical support. By means of the modern 

 method of starting with a single factor — single-seed plant- 

 ing — instead of with a quantity of seed, probably containing 

 several elementary and fixed species, all of which but one 

 had to be eliminated, it is considered that this support has 

 now been broken down, and that selection as applied in 

 agriculture is no longer an argument against the conception 

 of an origin of species by saltatory changes. 



Vegetation of the Antarctic Sea. 



.\ beginning has been made by C. Skottsberg, who ac- 

 companied the Swedish Antarctic Expedition of 1902, in the 

 Antarctic, to investigate the marine flora, in order to give 

 a true picture of its nature. Unfortunately, the most im- 

 portant collection of algje was lost with the ship. The places 

 visited belonging to the .\ntarctic proper were South Shet- 

 land Islands, coasts of Louis-Philippe Peninsula, Palmer 

 .\rchipelago, Ross Island, and the neighbourhood of Snow 

 Hill. The algal flora proved to be richer than was ex- 

 pected. The salinity and temperature of the sea are import- 

 ant factors, and exercise much influence on the development 

 of marine vegetation. In the .Arctic Sea the coast water of 

 Siberia mixes with a large amount of fresh water brought 

 down by the large rivers, and the poverty of the littoral 

 region is considered to be partly due to this fact. In the 

 -Antarctic Sea the conditions are different, no rivers are 

 known to exist, and the superfluous precipitation is dis- 

 charged in the form of icebergs. These are usually carried 

 some considerable distance to the north before they melt. 

 The salinity of Antarctic sea water slightly exceeds that of 

 the .Arctic Sea, the temperature of the two is about equal. 

 The temperature sinks and the salinity rises with increasing 

 depth. Ice also, to a great extent, determines the distribu- 

 tion, or even the presence of algae, which can only grow in 

 places where the beach is free from ice and snow during 

 the summer. During the winter a bank of ice and snow 

 reaches to high-water mark, and a continuation of this in 

 the form of an '' ice-foot " covers the greater portion of the 

 littoral region. Perennial algse live throughout the winter 

 in a frozen condition and deprived of light ; the calcareous 

 forms are especially able to endure in this condition through- 

 out the winter, but examples of the more delicate kinds were 

 also collected that had survived this treatment. In some 

 instances very thick ice remains unbroken for seven or eight 

 months in the Dundee .Strait, nevertheless, a rich vegetation 

 exists, proving that the Antarctic algse must possess the 

 power of living for months on the productions of the previ- 

 ous summer. Icebergs and drifting ice also prevent the 

 growth of algae ; in many places both littoral and sub- 

 littoral zones are quite polished by icefloes dashed against 

 the rocks by waves or tidal currents. 



Owing to the loss of the greater part of the collection, 

 the regional distribution of the marine flora could not be 

 worked out, nevertheless, littoral, sub-littoral, and deep- 

 water zones were found to possess characteristic species. 

 Calcareous algse are conspicuous in the littoral zone, species 

 of Iriilca are also in abundance. Dcsmare.itia occurs in pro- 

 fusion in the sub-littoral zone, and is as characteristic of the 

 .\nlarctic as the Lamiitaria formation is for the .Arctic. 

 Florideae arc characteristic of the deep-water zone, gigantic 

 specimens of (rracilaria (Lcptosarca) simplex, and many other 

 species of smaller size. Srhizoneura qucrcifolia occurred in 

 plenty; this species is related to Delesseria sinnata, occurring 

 the Ihe .\rctic .Sea. 



CHEMICAL. 



By C. AiNsvvoRTH Mitchell, H.A. (Oxon.), F.I.C. 



The Poison ivy. 



The latest addition to oui- know liilgr of the chemistry of 

 this curious plant is that published by Messrs. .Acree and 

 Syme in a recent number of the American Chemical Journal. 

 The poison ivy or poison oak (lihus toricodcndron) grows in 

 many parts of the United States and in Canada, and in the 



erect form reaches the height of about 40 inches. When in 

 the vicinity of trees or walls, however, it becomes parasitic, 

 and may then grow to a height of 30 feet or more. For 

 long this climbing variety was regarded as a separate 

 species, but the identity of the poison oak and poison ivy 

 has now been proved beyond question. Both produce small 

 green flowers and small white fruit, and contain a milky 

 juice which turns black on exposure to the air. The leaves 

 are employed commercially in the manufacture of a black 

 varnish stain for boots, being collected between May and 

 Julv while the plant is in bloom. Another curious property 

 of the juice is that it raises blisters when brought in con- 

 tact with the skin, while even the vapours given off by the 

 plant, especially by night, have the same effect upon certain 

 peculiarly susceptible people. For this reason the juice was 

 at one time a favoured remedy for certain skin complaints, 

 and is still used to some extent for the purpose in the 

 United States. The poison ivy was introduced into England 

 in 1640, but it was not until 1798 that it was tried as a 

 medicine in Europe, a doctor at Valenciennes being the first 



The Poison Ivy iRhtis toxuoJir.dron). 



to prescribe it to his patients. But long before then the 

 juice of the plant had been recommended as a marking ink. 

 Thus the .\bbe Mazeas, in a letter published in the 2'rn/i.s- 

 (ictions of the Boyal Society for 175S, describes his experi- 

 ments on this point, and states that characters written with 

 the juice upon his linen had remained quite black after 

 constant washing for live years. Incidentally it is men- 

 tioned that the plant was then growing in the gardens of 

 the Bishop of London's Palace at Fulham, but inquiries 

 made by the present writer show that it has long since 

 disappeared. Other writers have borne witness to the per- 

 manency of the stains produced by the juice upon linen. 

 The writing is quite proof against soap and water, dilute 

 acids, alkalies and bleaching powder, though it is easily 

 removed by ether. The juice is therefore still emploved in 

 the manufacture of marking inks in .\merica. Herbivorous 

 animals can e.it the poison ivy without ill effects*, but upon 

 dogs it acts as an irritant poison, producing convulsions 

 and death. There are also several cases on record of chil- 

 dren being poisoned through eating the berries. One of 



•Maiscli and Stille, NalioMal Diif>enialory. 



