November 19, 1908J 



NA TURE 



85 



illustraled by experiments with tlie ingenious apparatus 

 devised bv him for investigating the meclianical and 

 electrical responses universally exhibited by plants on 

 stimulation. 



Friday morning was occupied with a series of five papers 

 on photosynthesis by workers at Cambridge. The president 

 gave an introductory paper on photochemical action in the 

 test-tube and the leaf, which consisted of a short account 

 of the C|uantitative laws governing such chemical changes 

 in vilro, followed by an inquiry as to how far the con- 

 ditions under which photolysis of CO, takes place in the 

 leaf would allow these laws to come into action. 



.Mr. Thoday then read a paper on increase in dry weight 

 as a measure of assimilation. This is the first critical 

 examination of Sachs's classical method, with the object 

 of directly determining the nature and magnitude of possible 

 errors that the procedure involves. Many investigators have 

 used it confidingly, but recently it has been suggested that 

 the method gives uniformly too high results, possibly due 

 to fixation of water in the cell during insolation, in addition 

 to the formation of carbohydrates. Mr. Thoday has proved 

 that there is no such fixation of water by finding that 

 organic analysis of the increased carbon content makes it 

 clear that practically the whole increase of dry weight may 

 be reckoned as carbohydralo. I-'urther, it is shown that 

 the excessively high values sometimes obtained are really 

 due to another cause, na^iicly, to shrinkage of the leaf- 

 surface by transpiration. Records were exhibited showing 

 that an attacked leaf of sun-flower fluctuates in area to the 

 4'Xtent of 5 per cent, in the course of a few hours, shrink- 

 ing during periods of insolation, recovering when passing 

 t louds check the rate of transpiration. 



Following this Mr. A. M. .Smith gave an account of 

 his work on the factors influencing photosynthesis in water 

 plants. This work was carried out with an apparatus 

 designed by Dr. F. F. Blackman, in which a complete 

 knowledge of the whole amount of assimilation is obtained 

 by combining an analysis of the bubbles given off by the 

 assimilating plant with an estimation of the diminution in 

 CO, content of the water flowing over the plant. 



The magnitude of assimilation in relation to the amount 

 of dissolved CO, in the surrounding water was first in 

 vestigated, and it was found that the assimilation varied 

 proportionally with the CO, .supply until the limit set by 

 the temperature or light intensity (in the particular con- 

 ditions of experiment) was reached. No indication of an 

 optimum CO, content was found, .and assimilation onh' 

 begins to be depressed when the water is one-third saturated 

 with CO,. 



It was further shown that aquatic flowering plants 

 possessing an " internal atmosphere " can work up a 

 greater proportion of the CO, supply than an aquatic moss 

 (Fontinalis) which has no " internal atmosphere." 



Mr. Parkin communicated a paper on the carbohydrates 

 of the snowdrop leaf and their bearing on the first sugar 

 of photosynthesis. The work of Brown and Morris in 

 iSo.l on the carbohydrates of the leaf of Tropa;oIum brought 

 forward the new view that sucrose rather than glucose 

 plays the important part in the " up-grade " sugars of the 

 foliage leaf. In that leaf the sugar metabolism is com- 

 plicated by the fact that starch is abundantly present, and 

 from it glucose could arise by hydrolysis. In the snow- 

 drop starch never occurs, so that this leaf is a simpler 

 case for investigation. Sucrose, levulo,se, and dextrose were 

 found in abundance, and the fluctuations in their relative 

 amounts followed. With increasing assimilation the sucrose 

 steadily increases, while the amounts of levulose and dex- 

 trose remain fairly constant. This is interpreted as favour- 

 ing the view that sucrose is directly formed in photo- 

 synthesis and that the hexoses are formed from it bv 

 hydrolysis. 



This view falls more into line with the conception that 

 the first sugar is .split off from a complex protein aggregate 

 tlirm with Baeyer's view of progressive condensation front 

 formaldehj'de. 



A pap<T by Mr. J. M. F. Drunimond on the time factor 

 in assimilation was communicated by the president. Ex- 

 periments were made on the amount of assimilation taking 

 place in cut-off leaves in a chamber lighted by artificial 

 light continuously for several days. After a time the power 

 of assimilation diminishes, and the object of the work was 

 NO. 2038, VOL. 79] 



to find the precise explanation of this result. It was proved 

 that part of this diminution is due to accumulation of the 

 products of assimilation in the leaf, and that the power of 

 assimilation is regained after the leaf has been kept in the 

 dark for a period and has diminished its carbohydrate stores 

 by vigorous respiration. -^ second cause of diminished 

 assimilation is the ' shutting of the stomata by the high 

 general turgor of the epidermis brought about by the high 

 sugar content of the sap. This factor can be recognised 

 by the increased assimilation which immediately follows 

 incisions into the leaf or the application of dry air. The 

 effect of stomatal closure can be overcome by increasmg 

 the CO, supply in the air current through the chamber. 



Ecolosical Papers. 



Friday afternoon was occupied by two papers on the 

 woodlands of England, by Mr. Tansley and Dr. Moss re- 

 spectively. Mr. Tansley devoted the first portion of his 

 paper to an attempt to show that the great majority of 

 English woodlands are actually derived from natural woods, 

 and retain enough of their primitive character to be treated 

 as natural or semi-natural plant associations. He went on 

 to distinguish four great types of natural English wood- 

 land, determined bv soil cha'racters— the oak type, the oak- 

 bircli-heath type, the ash type, and the beech type— and to 

 explain the distribution, character, composition, and prm- 

 cipal subtypes of each of these. 



Dr. Moss, agreeing with Mr. Tansley 's main scheme of 

 classification, dealt especially with the woods of the 

 Pennines, on which he distinguished upland oak {Quercus 

 sessilillora) and birch w^oods, with transitions between 

 them. These, which occur on siliceous soils, he regarded 

 as differentiations of the oak-birch-heath type, according to 

 the factor of altitude. Opposed to these, and of essentially 

 different character, are the woods belonging to the ash 

 type, which occur on the mountain limestone of that 

 region. The woods of the lowlands of northern England 

 agree ecologically with those of the south, but the beech 

 type is entirely absent. 



' Prof. R. H.'Yapp gave an account of his observations on 

 the evaporating power of the air in different strata of 

 the marsh formation of Wicken Fen. The average evapora- 

 tion in the free air above the tallest plants is about 17 

 times that in the laver immediately below the tops of the 

 tallest plants, and 6-8 times that in a stratum 18 inches 

 below the surface of the vegetation and just above the soil- 

 level. 



Morphological and ralacobotanical Papers. 



On Tuesday morning Mr. W. C. Worsdell read a paper 

 on the origin of dicotyledons, in which he based his view- 

 of the phylogeny of this group on the doctrine of 

 ■• anaphytos'is," or the building up of the plant body from 

 a colony of distinct individuals or " phytons," budding one 

 from another as the stem grows in length. He held that 

 the facts of embryogeny in vascular plants are entirely 

 opposed to the ordinary view that the plant primarily con- 

 sists of a single shoot bearing leaves as lateral appendages. 

 The primary individual of the colony of phytons, as i-e- 

 presented by the embryo of the higher plant, is phylogenetic- 

 ally derived" from the'bryophytic sporogonium, of which the 

 capsule, seta, and foot correspond with the primary 

 phyllome, caulome, and root of the vascular plant. The 

 facts of embryonic segmentation and the dominance of the 

 cotyledonary organs were cited as being opposed to the 

 monaxial view, in which the stem is regarded as the 

 dominant org.-in and the leaves as appendages. F'rom this 

 position the author deduced the primitiveness of the mono- 

 cotyledonous type with its terminal cotyledon, _ which mitst 

 have preceded the dicotyledonous type, in opposition to Miss 

 Sargant's theory of the derivation of the monocotyledonous 

 from the dicotyledonous type by fusion of the two coty- 

 ledons. Anatomical evidence was adduced to show that 

 the scattered bundle arrangement of monocotyledons is 

 primitive, and that vestiges of this arrangement are found 

 in many dicotyledons. The absence of anatomical evidence 

 in seedlings pointing to such a conclusion vi-as attributed 

 to space-relationships. Finally, pleiomery of the flower was 

 recognised as primitive, and the prevailing trimery of mono- 

 cotyledons as reduced from such a condition. Mr. Wors- 

 dell's views were criticised, mainly from a hostile standpoint, 



