3-68 THE JOURNAL OF BOTANT 



external morphology of the stems of Calamites, with a revision of 

 the British species of Calamopliloios and Dictyocalatnites of the 

 Upper Carboniferous Age. Mrs. Arber read a paper on " The ' Law of 

 Loss ' in Evolution," of which the following is a summary : In the 

 course of a comparative study of aquatic Angiosperms, extending over 

 a number of years, the author has been led to recognize a certain 

 minor principle which seems operative in some phases of evolution. 

 It appears to be a general rule that a structure or organ once lost in 

 the course of phylogeny can never be regained ; if the organism 

 subsequently has occasion to replace it, it cannot be reproduced, but 

 must be constructed afresh in some different mode. The author 

 proposes to term this principle the " Law of Loss." This law is 

 obviously not susceptible of direct proof, bvit an attempt is made to 

 show that, if used as a working hypothesis, it throws light on a 

 number of structural features whose interpretation presents diffi- 

 culties on other theories. Some time after the author had deduced 

 the " Law of Loss " from a comparative study of living j^lants, she 

 learned that zoologists had already arrived at very similar conclusions 

 regarding Vertebrates from a study of their palseontological history. 

 Dollo's "Law of Irreversibility " covers much the same ground as the 

 " Law of Loss." The fact that the same principle has been recog- 

 nized independently for plants and for animals — in the one case 

 through a study of comparative morphology and in the other through 

 a consideration of actual historical evidence derived from fossil 

 records — seems to be an indication of the validity of the law. 



A SUPPLEMENT to the 'Proceedings of the Linnean Society for 

 1917-18 contains transcriptions by Dr. Da3alon Jackson of two 

 letters to Linnaeus from Tulbagh, Governor of the Dutch Colony at 

 the Cape from 1751 to 1771, including a list of the plants and bulbs 

 sent by the latter to the former about 1769. 



We have received the Thirty -fourth Anmial Heport of the 

 JVatson Eotunical Exchange Club, which will be noticed in an early 

 issue. 



Seyeeal communications — among them a paper on the Eoxburghs 

 by Sir David Prain, in which the conclusions arrived at in the article 

 headed " ' John ' Roxburgh " (p. 202) are rightly called in question — • 

 are unavoidably held over for want of space. For the same reason a 

 review of The Life and Letters of Sir Josejyh HooAer by Leonard 

 Huxley (Mui'ray, S6s. net) has been delayed, and it has been impos- 

 sible to conclude within the year Dr. Wernham's Monograph of 

 Manettia, begun as a supplement. With regard to this latter, it is 

 suggested that the existing pages should not be bound up with the 

 present volume but held over until next j'ear, when the paper will be 

 completed. It may be hoped that during the course of 1919 the 

 restrictions which have compelled the reduction of the Journal may 

 be removed, and that it will resume its pre- War dimensions. 



