452 



SCIENCE 



[N. S. Vol. XL. No. 1030 



more species together under one name. On the 

 other hand, to one of a more analytical bent of 

 mind, the difference between members of a single 

 species may appear so marked that he will be 

 under constant temptation to separate them into 

 still smaller subdivisions and to give to each spe- 

 cific rank. But, whichever course we follow, the 

 different groups into which the genus, or a species, 

 may be divided represent little more than particu- 

 lar tendencies or directions of variation, and the 

 members of each make up a series illustrating the 

 different stages. The word "species," as applied 

 to our North American asters, can hardly be said 

 to have any other significance than this. 



It will startle some old-fashioned taxonom- 

 ists to read the next sentence: 



It does not seem a valid objection that under 

 such a definition a single plant might be conceived 

 as belonging to more than one species. 



Notes are made of ten previous lists of 

 Wisconsin asters, and then follows a systematic 

 and critical discussion of the species recog- 

 nized by the author. This latter is so well 

 done that one is tempted to wish that it might 

 be used as a model by other local botanists. 



SHORT NOTES 



Important phytopathological papers by G. G. 

 .Hedgcock have appeared as follows: "Notes 

 on Some Western Uredineae which attack For- 

 est Trees " {Phytopath., III.) ; " Notes on 

 Some Diseases of Trees in our National 

 Forests " (Phyiopath., III.) ; " Injury by 

 Smelter Smoke in Southeastern Tennessee" 

 (Jour. Wash. Ac. 8ci., IV.) ; " The Alternate 

 Stage of Peridermium pyriforme " (privately 

 printed June 12, 1914). In the latter the eon- 

 elusion is reached that the alternate stage 

 occurs on Gomandra umbellata. 



B. F. LuTMAN contributes an interesting 

 paper on " The Pathological Anatomy of 

 Potato Scab " accompanied with ten text 

 figures, in which he concludes that " The scab 

 is due to the hypertrophy of the cells of the 

 cork cambium" (Phytopath., III.). The same 

 author's " Studies on Club-root " (Bull. 175, 

 Vt. Agr'l Expt. Sta.) will be suggestive to 

 those who are interested in the organisms usu- 

 ally known as slime molds (Myxomycetes). 

 The one here under consideration is Plasmo- 



diophora hrassicae, and it infests the root cells 

 of cabbages and other cruciferous plants. It 

 gains entrance either through the epidermis 

 or the root-hairs, and produces cellular hyper- 

 trophy, especially of the cortical tissues. 



Nuclear divisions in the Plasmodium are of two 

 types — vegetative and reduction. The vegetative 

 divisions are peculiar in that a spireme is not 

 formed. . . . The reduction division is one of those 

 preceding spore formation, probably the first. 



Six text figures and four plates (with 52 

 figures) accompany the twenty-seven pages of 

 text. 



A SIGNIFICANT feature of the new edition of 

 the " Genera of British Plants," by H. G. 

 Garter (Cambridge, 1913), is the adoption of 

 Engler's system. At the outset it must be 

 remembered that the " plants " referred to in 

 the title are the ferns and flowering plants. 

 The little book (of 139 pages) 

 is intended to familiarize students of British vascu- 

 lar plants with Engler's system in its latest form, 

 and thus to habituate British floristie students to 

 the use of a more natural system than that to which 

 they have been accustomed in the British floras that 

 have hitherto appeared. 



In carrying out this plan the class, ordinal 

 and family characters are clearly given, while 

 the genera are briefly characterized by means 

 of analytic keys. A similar book for North 

 America would be very useful. However, we 

 can not approve of the use of the terms 

 " apopetalous " and " apochlamydeous " as 

 defined by the author (petals, or perianth 

 " absent by reduction ") even though sanc- 

 tioned by Engler. Certainly " apetalous " and 

 " achlamydeous " are sufficiently definite for the 

 conditions of no petals, and no perianth, 

 leaving " apopetalous," and " apochlamydeous " 

 for the conditions of separate petals, and 

 separate perianth segments. 



Charles E. Besset 

 The UNrvEESiTY or Nebraska 



SPECIAL ASTICLES 



THE ALLEGED DANGERS TO THE EYE FROM 



ULTRA-TIOLET RADIATION 



During recent years there have been not a 

 few sensational attacks upon modem illu- 



