Eoyal Microscopical Sociehj. 93 



plants ; and in the first volume of tlie * Annals Nat. Hist.' he gives a 

 detailed account of the statement above referred to, viz. the existence 

 of spiral vessels in the roots of dicotyledonous plants, contrary to the 

 hitherto received opinion of English botanists. They had been in 

 the habit of considering spu'al vessels as peculiar to the structure of 

 monocotyledonous roots ; and as pro\Tng a distinctive character be- 

 tween the root and stem of dicotyledons, he says, " So thoroughly has 

 this opinion of their position gained credit that I have in no case 

 been able to remove it but by giving ocular demonstration that it is 

 in opposition to facts." 



It was in 1837 also, whilst making some photographic experi- 

 ments with the solar microscope, he discovered a mode hitherto un- 

 attained of separating the rays of heat fi'om those of light, so as to 

 enable pictures to be taken with cemented achromatic objectives with 

 safety, and it was at this time he made the first micro-photographs ; 

 the best known of these are the head of a flea, and the section of the 

 tooth of the Lamma, which were subsequently lithographed : a copy 

 of that of the flea he has left to the Society, that of the Lamma 

 forms one of the series selected by Owen for his Odontography ; 

 and it was whilst making these experiments that he discovered the 

 value of gallic acid as a sensitizer, and hyposulphite of soda as a 

 fixer on prepared paper, which stamps him as one of the foremost 

 pioneers in the development of photography. 



In the ' Annals Mag. of Nat. Hist.,' 1838, vol. ii., there is a 

 paper by him " On some New Organic Eemains in the FHnt of 

 Chalk," the object of which was to show more particularly the 

 fossil contents of flint pebbles and flint nodules of the chalk, and 

 to examine whether the flints of different strata had or had not a 

 common origin. He found that Xanthidiae were absent in the 

 Brighton pebbles, whilst several species occurred in the flint of 

 Kent and Sm'rey. Besides these singular remains which Ehren- 

 berg had previously described, the author detected the scales of the 

 ctenoid and cycloid orders of fishes which have not yet been found 

 in earlier formations. For comparison, illustrations of scales of 

 existing fish accompany the paper, and these were supplied to the 

 author by JMr. TarreU. 



It was in this year (1838) that he was elected a Fellow of the 

 Koyal Society, and it was about this time that he drew the special 

 attention of microscopists so strongly to the great value of black- 

 ground illumination, that it has (though previously known) since 

 gone by his name. In the first volume of the ' Transactions of the 

 Microscopical Society ' is a paper which he read before the Society, 

 headed " The Process of charring Vegetable Tissue as applied to 

 the Examination of the Stomata of Garden Ehubarb," in which he 

 advocates the importance of the plan for determining the form and 

 character of cells and cellular tissue, &c., and also as enabling the 



