HARDVVICKE'S SCIENCE-GOSSIP. 



13 



take this volume to be the best specimen of the kind 

 of labour in which they are engaged. It contains a 

 list of all the species and varieties of flowering 

 plants, ferns, &c, growing in the Cuckmere district, 

 East Sussex, and is illustrated by a geological map, 

 by means of which we can trace the influence on 

 the local geographical distribution of plants by 

 geological conditions. To local botauists this book 

 will be a welcome boon, and we congratulate Mr. 

 Roper on the successful manner in which he has 

 worked out the botanical details. The introduction 

 to this work is exceedingly goo I, well written, and 

 presents all the conclusions that can be drawn re- 

 lative to the distribution, &c, of the plants, very 

 clearly indeed. 



The Guernsey Isoetes.— In Science-Gossip 

 for November, p. 25S, I stated that this plaut, 

 first noticed in Science-Gossip in 1S73, p. 1T3> 

 might be the I. Hystrix Duriei, but certainly not 

 the /. Hystrix, Bory, of Algiers ; Mr. Baker, Curator 

 of the Kew Herbarium, quite confirms this state- 

 ment. He tells me that the Guernsey plant is /. 

 Hystrix,va,v.subinermis (uuarmed, spineless), Durieu, 

 ■in "Balansa PI. Alg. Exs.," 1S51, No. 27, adding, " We 

 have the same form in Kew Herbarium from 

 Caprera, Algeria, French Landes, Phrygia, Smyrna, 

 Castile, &c. ; it is, in fact, more common than the 

 typical Hystrix with the big spines, as photographed 

 by you." Again, he says, " Best differential cha- 

 racter of Isoetes Duriei and Hystrix is in the 

 raacrospores (see specimens enclosed)." In the 

 description of the Isoetes by Grenier and Godron, 

 it is stated that the different species are chiefly dis- 

 tinguished by the two sorts of sporanges, one with 

 macrosporocarpes situate at the axils of the external 

 leaves, containing from 40 to 230 macrosporauges 

 in each sporocarpe ; the other with microsporo- 

 carpes situate at the axils of the interior leaves, 

 containing above 1,000,003 microsporanges in each 

 sporocarpe, resembling fine flour (fine farine). If, 

 therefore, the different species are to be determined 

 by the formation and characters of the macrospo- 

 rauges, a very powerful microscope must be used in 

 the examination of them. All the macrosporauges 

 described by Grenier aud Godron are stated to be 

 more or less tubercled, except /. Hystrix, which is 

 very finely reticulated, showing the differential cha- 

 racter referred to by Mr. Baker. I am not aware 

 that the anatomy of any of the Isoetes has been 

 drawn or engraved, except the 1". lacustris in 

 Sowerby, and in plate 12 of Hooker and Arnott's 

 " British Flora " ; or that with the exception of the 

 /. lacustris, figured in Sowerby and in Science- 

 ■Gossip for 1S73, p. 51, and the Algerian plants in 

 the "Floraof Algeria" (a work rarely to be met with, 

 and which I have for some time endeavoured in 

 vain to obtain both in London and Paris), a copy of 

 which may be seen in the Library at Kew ; with 



these exceptions, I am not aware of figures of any 

 entire plant of Isoetes (except also the plants illus- 

 trated in the last number of Science-Gossip) having 

 been engraved and published. The total absence of 

 spines in the /. Hystrix subinermis Duriei, give3 it 

 externally such a different appearance from the 

 typical plaut (I. Hystrix, Bory), that no one could 

 take them to belong to the same species without 

 examining the macrosporauges. I presume the 7. 

 Hystrix, var. biennis, had not been discovered in 

 France in 1855, the date of Grenier and Godron's 

 " French Flora," or it would have been noticed 

 by them; and the same reason would account for 

 its not appearing iu the "Flora of Algeria," where 

 it no doubt was discovered subsequently.. — T. B. IF., 

 Brighton. 



Flora, of Rodriguez. — In his recent address to 

 the Royal Society, Dr. Hooker referred to Mr. 

 Balfour's report on the "Flora of Rodriguez," and 

 stated it as a very remarkable fact that one of the 

 two new genera of flowering plants which have been 

 found belonging to the natural order Turneracea, is 

 most closely allied to a peculiar Panama genus ; and 

 that one of the new species has only a single con- 

 gener, which is a Pacific Island plant. 



Botany for Schools.— A nicely got-up little 

 elementary volume on Botany, intended for schools 

 and science classes, and compiled by Mr. H. J. 

 Browne, MA., has just been published by Messrs. 

 Mullan, of Belfast. It deals principally with struc- 

 tural botany, but gives an outline, with useful but 

 brief descriptions, of cla-.siQcatory botany as well. 



GEOLOGY. 



The Origin of the Primary Rocks.— A.t the 

 last meeting of the Geological Society of London, a 

 paper ou " The Physical Conditions uuder which the 

 Upp3r Silurian and succeeding Palaeozoic Rocks 

 were probably deposited over the Northern Hemi- 

 sphere," was read by Henry Hicks, F.G.S. The 

 author, after pointing out the lines of depression 

 explained in his former paper To the Society, now 

 further elaborated the views then propounded by 

 him, by carrying his examination into the higher 

 Palaeozoic series and into more extensive areas. 

 Beginning at the top of the Lower Silurian, where he 

 first recognizes the evidence of a break in the 

 Palaeozoic rocks, he proceeded to show that this 

 break was restricted to very limited areas, and 

 almost entirely confined to the parts which had been 

 first submerged, and where the greatest thickness 

 of sediment had accumulated on both sides of the 

 Atlantic, and hence where the pre-Cambrian crust 

 had become thinnest. On the European side this 

 break occurred where volcanic action had taken 

 place, and has doubtless to be attributed to the 



