326 



NATURE 



IJuly 25, 1878 



1,663 species, according to a statement in the Bulletin 

 of the Torrey Botanical Club of New York (May, 1878), 

 which contains a justly appreciative notice of the work. 

 The preface states that the whole will be completed in 

 two volumes of 1,200 pages each, which, if the forth- 

 coming parts contain as many species as that now before 

 us, would imply that the known phasnogamic floras of the 

 area embraced consists of about 10,000 species, a rather 

 larger number than is included in Nyman's "Sylloge 

 Florae Europese," published in 1855, which contains 

 9,738. 



If this latter number represents even approximately 

 the extent of the European Flora, it shows that Europe 

 contains, in proportion to its area and latitude, more 

 plants than temperate North America : for its area 

 (3,600,000 square miles) but little exceeds that of North 

 America, exclusive of the vast British possessions, whilst 

 Ihe United States extends almost into the tropics and 

 contains many subtropical plants. This superior botanical 

 richness of Europe is no doubt due to the great diversity 

 of the floras of its three southern peninsulas, Spain, Italy, 

 and Greece, and to the number of species in its central 

 mountains ; as also to the prevalence of annuals, in 

 which Europe far outnumbers any other continent. On 

 the other hand, Dr. Gray's views of the limitation of 

 species are no doubt large, compared with that adopted 

 by Dr. Nyman. 



Before concluding this notice of Dr. Gray's work, we 

 may notice the identification of the North American 

 Solanum Fendleri^ Gray, with the potato {S. tuberosum) as 

 var. boreale, thus giving this esculent a range from Chili 

 and Buenos Ayres to the United States. 



Mr. Watson's " Bibliographical Index to North Ameri- 

 <:an Botany" is not a mere compilation, as its title would 

 make it appear, but a first-rate contribution to botanical 

 science ; the authorities cited being in all possible cases 

 verified by a reference to the works themselves, and often 

 by a critical study of the specimens by a botanist of 

 scrupulous exactness, who is also well acquainted with 

 the North American Flora, as collaborator with Asa Gray 

 in the herbarium at Harvard. The first part, now 

 published, includes the Polypetalous Dicotyledons, thus 

 covering the ground of the first volume of Torrey and 

 Gray's " Flora of North America," published in 1838-40. 

 Next to Gray's Synoptical Flora this is the greatest boon 

 •lo systematists that has appeared in North America for 

 many a year, and it is further a necessary adjunct to the 

 Synoptical Flora, containing as it does a mass of citations 

 of descriptions and plates, of which that work is thus 

 relieved. 



It is further very interesting as showing the additions 

 made to North American Botany since the publication 

 of Torrey and Gray's above-mentioned first volume. 

 Taking ten of the most considerable American orders of 

 Polypetalas, we find that in 1 840 these included 262 genera 

 and 1,267 species, to which have been added in the 

 thirty-seven years that have elapsed since that period, 

 only 12 genera, but 756 species. In so far as this affords 

 the means of forming a rough estimate, it shows that the 

 discoveries during the period in question, and which are 

 almost confined to the southern and western States, have 

 added about one-third to the previously known North 

 American flora. These additions affect the different orders 



very variously, as might be expected ; thus, whilst the 

 increments to some, as Rattunculacece (20) and Caryo- 

 phyllecs (16) are small, and of others moderate, as 

 Onagrmice (24), Rosacea: (28), and Saxifragece (10), those 

 of UmbellifercB (45) are large ; the orders Cruci/erce (95) 

 and OnagraricB (47) have been nearly doubled, Leguminosce 

 (360) more than doubled; and to Cacti, of which but nine 

 species were known at the first period, in have since 

 been added ! 



In two comparatively unimportant matters of con- 

 venience the author has departed from usage, and, we 

 think, without good cause ; the genera and species are not 

 numbered either in Gray's or Watson's work, on what 

 grounds we cannot imagine. To have to run up the 

 numbers of the large genera (as Astragalus), for the pur- 

 pose of comparing or contrasting the items of the American 

 flora with those of others, involves a grievous loss of time 

 to the botanist, whilst for the arrangement of herbaria, 

 and ready reference in it to these standard books, the 

 numbering would have been very useful. The other 

 departure is the alphabetical arrangement of the genera 

 under the orders in the "Bibliography," which, in the 

 case of genera absorbed, necessitates a reference to the 

 index. 



If a few copies, with the matter printed on one side of 

 the page, could have been obtained by botanists, it 

 would have been a great boon. In such a case the pages 

 of the "Bibliography" might have been intercalated 

 with those of Gray's "Synoptical Flora;" and each 

 species, with its references, might have been cut out and 

 attached to the herbarium specimens of the species. 



It remains to wish these able and industrious authors 

 successfully through the works they have so well begun. 



J. D. Hooker 



THE HYDROIDS OF THE GULF STREAM 

 Report on the Hydroida collected during the Exploration 



of the Gulf Stream by L. F. de Pourtalh. By G. J. 



Allman, M.D., F,R.S., President of the Linnean 



Society. (Cambridge, U.S., 1877.) 

 This report forms No. 2, vol. ii. of the quarto memoirs 

 of the Museum of Comparative Zoology at Harvard 

 College, and has been published by permission of the 

 Superintendent of the United States Coast Survey, and 

 is illustrated by thirty-four plates. It forms one of the 

 most important contributions to the natural history of the 

 hydroids that have appeared of late years, and it de- 

 scribes a very large number of most interesting and new 

 forms. One of the sub-orders of the hydroida is well 

 characterised by having the hydroids quite unprotected — 

 not covered by any external protective receptacle. In 

 this sub-order (Gymnoblastea) but nine species were 

 found in Pourtal^s' collection. Although they are all re- 

 ferable to known genera, yet all of them are new. The 

 great bulk of the collection belonged, however, to another 

 sub-order, in which the hydroids are provided with ex- 

 ternal protective receptacles (hydrotheca), and which is 

 more or less familiar to us as containing the Cam- 

 panularian and Sertularian forms. Of this sub-order 

 (Calyptoblastea) some fifty-six species are described, 

 and among the Sertularinas no less than seven new 

 genera are described, with forty-two new species out of 

 a total of forty-three. Among the Campanularinse two 



