380 AN INTRODUCTION TO THK STUDY OF SEA- WEEDS. 



" Variations do not arise accidentally or spontaneously in 

 nature, as long as the same environment is maintained." Has 

 Mr. Henslow studied Potamogetons ? Is not a water environment 

 more constant than a land one? and yet several genera (e. g., Naias, 

 Potaiiinffctoii) afford excellent examples of variation among mature 

 individuals. Perhaps Mr. Henslow falls back on the hybrid theory, 

 though we do not remember to have come across it in his book. 

 Among a number of plants growing together, e.r/., chicory by the 

 side of a field, rme will produce a white flower. It will be at least 

 as difficult to prove that this is due to a change in environment as 

 that it is a mere accidental variation. 



The author also adduces as evidence the occurrence in Malta 

 (i. c, a changed environment) of forms or varieties of British 

 species ; and instances (p. 21) four forms of chickweed which differ 

 in the relative size of petals and calyx and the number of stamens. 

 Here again the argument is extremely incomplete, and may be 

 used against Mr. Henslow. Do all these four forms grow in 

 similar localities, or in those sufficiently different to afford the 

 required change of environment ? This should have been stated. 

 On the next page he says, " The question as to one variety issuing 

 from a species in the same environment may be shown to be a 

 irductio ad abs^irdiwi,'' by taking extreme cases. But it is equally 

 absurd to imagine a change of environment from Britain to Malta 

 giving rise to four forms in which the stamens vary in number 

 between two and ten, and the petals from complete absence to a 

 size which has called forth the term " [/randi/Iora." If variation is 

 quite definite, and only a response of the protoplasm to the environ- 

 ment, how is it that in the same environment we find, for instance, 

 such very different adaptations as those occurring in the desert — 

 large succulent leafless cacti or euphorbia, hard dry woody spiny 

 glabrous acacias, or densely hairy species ? Or, on the other hand, 

 the same response under such totally opposite conditions as desert 

 and water — for spiny leaves are very characteristic of water plants 

 (e.g., Lagarosiplum, Hydrilla, Elodea, Naias, &c.). 



Mr. Henslow's little book is of value in that he has brought 

 together a large number of facts illustrating the strnctaral pecu- 

 liarities of desert (already published in the Journal of the Linnean 

 Society), alpine, arctic, aquatic, or climbing plants, and also the 

 existence of a certain plasticity in plants; but we cannot hear in it 

 the death-knell of Natural Selection. Mr. Henslow's difficulty is 

 that you cannot see Natural Selection working. But this is no proof 

 that it does not work. p^ ^ Rendle. 



All Introduction to the Study of Sea-iveeds. By George Murray, 

 F.K.S.E., F.L.S. 8 coloured plates and 88 other illustrations. 

 Pp. xvi, 271. Macmillan & Co. 1895. 7s. 6d. 



During the fifty years which have elapsed since the publication 

 of Harvey's great work — Phycolnyia Britannica — great advances in 

 the knowledge of British and other sea-weeds have been made. 

 Not all would-be students are able to consult the continental works 

 where many of these advances are embodied, and there was great 



