NATURE 



31; 



THURSDAY, FEBRUARY 6, ic 



TRANSPIR.iriON AND ANATOMICAL 

 STRUCTURE IN TROPICAL PLANTS. 



Der Einfluss des Kliiiias auf den Bau der Pflanzen- 

 Xewebe. Anatomisch-physiologische U ntersitchim gen 

 in den Tropen. By Dr. Carl Holtermann. Pp. 

 viii + 249; plates. (Leipzig: W. Engelmann, 1907.) 

 Price 12 marks. 



DR. HOL'rF:RM.\NN\S investigalions, mainly 

 carried out in Ceylon, include a long series of 

 experiments on the transpiration of different tropical 

 plants. His tables show great variations in the 

 ,Tmount of transpiration for the same plant during the 

 same hours of different days, and these are in many 

 cases not explained by the differing temperature and 

 relative humidity, which are the only other data given. 

 Thus, for instance, in the case of Caniia indica, be- 

 twven q.40 a.m. and 5.40 p.m. on January 11 (with 

 a relative humidity of 61 and a temperature of 25°'4 

 at 10 a.m.). the transpiration was o"37 gr. per hour 

 per sq. dm. of leaf surface, while on January 17, 

 between q.45 a.m. and 5.30 p.m. (R.H. 63, temp. 

 26°-2, at 1 1. 15 a.m.), the transpiration was 0^92 gr. 

 ■per hour per sq. dm., and on January 18 between 9.15 

 ti.m. and 3.30 p.m. the transpiration was 2"6o gr. per 

 hour per sq. dm. (no humidity or temperature data 

 .ire given within the period of the experiment, but 

 judging from the late afternoon figures the day did 

 not ditYer much from the others). This, though an 

 ■e.Ktreme case, is only one out of several similar ones, 

 and the effect of such figures on the reader is de- 

 cidedly bewildering, though the striking variations 

 may be explicable by changes of insolation, or the 

 irregular occurrence of drying winds. .As they stand, 

 the author's figures only demonstrate that the tr.-ms- 

 piration of the plants studied exhibited startlinglv wide 

 fluctuations which remain quite unexplained. 



The author's general conclusion from his experi- 

 ments is that while the highest transpiration figures 

 per hour in the tropics are considerably higher than 

 any north European ones, yet active transpiration 

 begins later and stops earlier in the day in the case of 

 a damp tropical climate, so that the daily average 

 is no higher than in Europe, while in the wet season 

 transpiration may cease for weeks at a time. He 

 thus does not disagree with the conclusions either of 

 Maberlandt or of Giltay on this question. Dr. Holter- 

 mann holds that water-tissue is essentiallv an arrange- 

 ment to supply water to the transpiring tissues during 

 these short periods of excessive evaporation, not a 

 means of lessening transpiration, and this view he 

 supports by showing that it is especially developed in 

 actively transpiring plants liable to be subjected to 

 these sudden demands. It is characteristic of the 

 leaves of tropical plants growing in a climate which 

 is neither quite xerophytic nor constantiv moist, and 

 this harmonises with the short daily period of verv 

 active transpiration already mentioned. The man- 

 groves, which ordinarily possess characteristic water 

 NO. 1997, VOL. ■Jj'l 



tissue well developed, form much less or none at all 

 in the leaves of examples cultivated in garden soil, 

 which transpire very much more freely than plants 

 growing in the natural salty soil. If these plants 

 cultivated without salt are now viatered with 3 per 

 cent, salt solution and placed in the sun, they show 

 a wilting of the leaves, and the mesophyll becomes 

 shrivelled. Mangroves growing in their natural 

 habitat also show wilting on hot afternoons, but only 

 the water-tissue is partially emptied and the leaves 

 recover during the night. For the rest the author 

 holds that the .xerophily of mangroves and of other 

 halophytes has been much overrated by Schimper and 

 others. They are scarcely, if at all, more protected in 

 this respect than many trees growing in similar situa- 

 tions but not in a salty soil. 



Dr. Holtermann describes three other formations 

 of strand-plants besides the mangroves, viz., first the 

 plants of moist sand, which fall into two categories, 

 (i) those growing on the edge of the sea, absorbing 

 salt water, and possessing water-tissue ; (2) those 

 growing further from the sea, with fresh bottom- 

 water, which have no special .xerophilous adaptations. 

 Secondly, the dune plants, a highly xerophilous type; 

 and, thirdly, the plants growing on salty mud, which 

 have internal water-tissue, and resemble succulent 

 desert-plants in many anatomical features. These 

 three formations have close parallels among the strand 

 formations of temperate regions. This classification 

 is good so far as it goes, but it ignores the beach- 

 jungle (Barringtonia-formation of Schimper), which 

 thj author apparently includes with the damp lowland 

 forest type. Yet this formation, though not well 

 developed in Ceylon, certainly has an independent 

 existence ; it is much in need of exact study and 

 delimitation. 



The author goes on to describe the damp lowland 

 woods, the dry plains of the north and east, and the 

 upland vegetation, as also the epiphytes and parasites 

 of Cevlon. Manv interesting observations are con- 

 tained in this part of the work. Dr. Holtermann also 

 discusses at some length the question of leaf-fall in 

 the tropics, and concludes that though it is a here- 

 ditary character, it is, in the endemic species, deter- 

 mined by the dry season, and, in general, leaves fall 

 when their structure does not fit them to withstand 

 the conditions prevailing during the time the trees are 

 bare. A similar explanation is given of the occurrence 

 of annual rings of growth in the wood, the author 

 relating the renewed formation of wide xylem ele- 

 ments to the increased transpiration taking place 

 when a crop of voung leaves is produced. 



The final section of the work is devoted to a dis- 

 cussion of " Direct Adaptation," in the course of 

 which an account is given of many interesting experi- 

 ments which add considerably to our knowledge of 

 adaptive reactions under new conditions. The author 

 rightly classes all these as phenomena of irritability, 

 but draws the conclusion that such characters, ac- 

 quired during the lifetime of the individual, can in 

 process of time be fixed and inherited. This con- 

 clusion is, of course, wholly unwarranted ; in fact, it 

 is totally irrelevant. .And meanwhile the mysterv of 



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