436 



NA TURE 



[March 8, 1906 



e.g. that of Lamarck, his estimate is by no means 

 that which many authoritative writers have expressed. 

 As we lay aside the volume some general reflections 

 remain convincingly with us — that the history of 

 biology is a rational evolution, and at the same time 

 inextricably intertwined with social evolution ; that 

 the same general ideas are re-incarnated century after 

 century in more evolved forms ; that each generation 

 meets the same old difficulties on a higher turn of the 

 spiral ; that clearly thought-out conceptions which 

 seem for a time to be vanquished re-assert themselves 

 with renewed vigour, and find their nosition in a more 

 complete synthesis. The modern biologist, intent on 

 new discoveries, has no use for Aristotle, Descartes, 

 and Leibnitz, but their influence may be upon him 

 none the less. In speaking of the aqueduct of Sylvius, 

 the Malpighian tubules, the Graafian follicle, or the 

 Cuvierian organs, we quaintly acknowledge our debt 

 to the past, but perhaps we betray our indebtedness 

 more when we are least conscious of it, for even the 

 most modern system of biology is, like our own body, 

 a veritable museum of relics. J. A. T. 



STOMATA AND PHYLOGENY. 

 Der Spaltoffnun gsapparat im Lichte der Phylogenie. 

 Ein Beitrag zur " phylogenetischen Pflanzenhist- 

 ologie." By Dr. Otto Porsch. Pp. xiv+196. 

 (Jena : Gustav Fischer, 1905.) Price 8 marks. 



THIS work, as its title announces, is an attempt 

 to use the stoma as a mark of relationship, and 

 thus to make it serve as a guide to the phylogeny of 

 plants. The author is filled with a pleasant enthusiasm 

 for his subject, and this he contrives to convey 

 to his readers, who, whether or no they are in com- 

 plete agreement with his views, will not deny that 

 he has produced an interesting and suggestive book. 

 Personally, we think he has done more, and that his 

 work has decided value. He begins by showing 

 (what has to some extent been shown before) that 

 definite types of stoma run through certain classes 

 or natural orders. He makes it clear that these types 

 remain recognisable even in plants exposed to various 

 environments. The gymnospermous type, for in- 

 stance, occurs in plants of such diverse habit as 

 Bowenia, Gingko, Dioon, and Gnetum. 



The author allows that the gymnosperm type is 

 essentially a stoma adapted to xerophytic conditions. 

 This brings us face to face with what is a difficulty 

 in inquiries of this sort — namely, how far persistence 

 of type is due to adaptation. This is especially difficult 

 in regard to the xerophytic habit, because our know- 

 ledge of the conditions which make this habit of value 

 is recent, and probably incomplete. It is only com- 

 paratively lately that conditions of life in a salt-marsh, 

 an English heath, and in the alpine regions of the 

 tropics have been recognised as equivalent environ- 

 ments in regard to transpiration. The author is, how- 

 ever, fully aware of the difficulty in question. 



It is interesting to find the gymnospermous stoma 



occurring in Casuarina, a genus known to possess 



morphological characters which have suggested that 



it may be an offshoot from an ancestor common to 



NO. 1897, VOL. Jl,] 



gymnosperms and angiosperms. In concluding this 

 section the author has some remarks on the minuter 

 taxonomic value of the stoma, e.g. in Dasylirion, 

 where the stomatal characteristics may be used to dis- 

 tinguish the species. He also directs attention to the 

 Commelinaceas and Eriocaulaceae, and to the genus 

 Eucalyptus, in all of which the stoma is characteristic. 

 As showing the possible value of the stoma to the 

 palajobotanist he quotes the case of a fossil Potamo- 

 geton recently shown by its stomatal type to belong to 

 the Loranthaceae. Porsch gives an interesting account 

 of reduced and rudimentary stomata in the true leaves 

 of Ruscus, in parasites, and in submerged plants. 

 The latter case is especially interesting because here 

 the stomata can hardly be of use for gaseous ex-- 

 change. But in the petals of flowers or the bulky 

 stems of holoparasites it is clear that they may be 

 of importance for respiration. This is a function of 

 the stoma which Porsch does not sufficiently discuss ; 

 thus in referring to the stomata of petals he considers 

 transpiration alone. The fact that large petals occur 

 devoid of stomata while others (Galtonia) have perfect 

 ones shows that the question is in need of physio- 

 logical inquiry. 



In another interesting section the author describes 

 the stomata of seedling leaves, which are generally 

 of an undifferentiated type, even when the adult 

 leaves have highly specialised stomata, e.g. in Hakea, 

 Spartium junceum, &c. This seems at first sight a 

 case of " recapitulation," but the author is careful to 

 supply an alternative view, viz. that in the early 

 stages of existence a plant is less subject to drought, 

 so that the simple stomata of the seedling may be an 

 adaptation to conditions less rigorous than those to 

 which the adult is exposed. The author, however, 

 accepts, with certain reservations, the recapitulation 

 point of view. 



The last section of the book deals with stomata in 

 relation to alternate generation. Porsch holds (with 

 Wettstein) the sporophyte to be an adaptation to life 

 on dry land in contrast to the gametophyte, which 

 retains aquatic characters. Taking the Bryophytes as 

 the lowest class in which stomata occur, he again 

 follows Wettstein in placing the mosses in the lower 

 division, the liverworts being a more specialised 

 form. It is in harmony with this view that in the 

 mosses stomata should occur only in the sporophyte. 

 Among the normal two-celled stomata are occasionally 

 found others of the four-celled type. This he looks 

 on as a " reminiscence " of an earlier form, in which 

 the intercellular spaces open externally in the simplest 

 manner between four epidermic cells. 



In the liverworts, on the other hand, the gameto- 

 phyte possesses openings which function as stomata. 

 There is only one group in the liverworts which 

 exhibits a highly organised sporophyte, and here in 

 Anthoceros we find true stomata having a pair of 

 guard cells, which are probably of a higher type than 

 occurs elsewhere among the Bryophytes. 



Among the Pteridophytes the most interesting fact 

 is that the stomata are of a type that may be supposed 

 to be the forerunner of the gymnospermous stoma. 

 The characteristic lignification is not always present 



