60 



KNOWLEDGE. 



February, 1913. 



requiring much moisture occur along streams. Apart from 

 these, the specialised forms which are more or less active 

 during the dry seasons comprise two types — the sclerophyllous 

 and the succulent. 



The sclerophyllous type iucludes a large number of woody 

 and spiny herbs and shrubs with reduced branches, restricted 

 foliage, and hardened surfaces. These xerophytes have a 

 very small water-balance, and the cell-sap often shows great 

 concentration — sometimes over one hundred atmospheres of 

 osmotic pressure. The specialisations shown by sclerophyllous 

 forms are of a direct physiological character, and entail the 

 least change in habit and structure. 



The succulents show most of the external features of the 

 spinose xerophytes, which may be carried to extreme limits, 

 as in the Cacti where the entire shoot may be reduced to a 

 short cylindrical or globose form, while there is great increase 

 in the extent of the pith and cortex enabling the plant to carry 

 a large water-balance. The cell-sap of succulents usually 

 shows a comparatively low osmotic pressure — rarely more 

 than about ten atmospheres, though it may increase greatly 

 with desiccation. 



The author describes experiments in which various plants 

 were subjected to desiccation, and the effects of depletion of 

 the water-balance noted. The large tree Cactus iCarncgiea 

 gigantea) may survive for a year or even more without 

 receiving additional water from the soil, but flowers are not 

 formed in the arid fore-summer unless the plant has received 

 its supply of water during the previous winter rainy season, 

 nor would apical growth ensue in midsummer unless the 

 summer rains were available. In Echinocactus both root 

 development and apical growth of the stem, with some 

 capacity for flower formation as well, were shown after one or 

 even two years of depletion of the water-balance ; individuals 

 exposed to the full intensity of the Arizona sunlight might not 

 survive for more than a year, though even the slightest 

 amount of shade would greatly enhance the value of the 

 enormous water-balance ; plants in an ordinary room were 

 in good condition after three years of deprivation of water. The 

 flattened Opuntias may exist for two or three years without a 

 water-supply, and may carry out seed-formation during this 

 period ; new joints may be formed, but usually at the expense 

 of the older ones, which are destroyed during the process. 

 In most of the plants experimented with, no notable changes 

 in structure were shown as the result of depletion of the 

 water-balance, except that the new organs formed were 

 usually of minimum size. The stems of Dioscorea, how- 

 ever, showed changes tending to the sclerophyllous habit. 



Five possible causes are suggested as influencing the rate 

 of water-loss by transpiration in a succulent exposed to desic- 

 cation. (1) The increased concentration of the sap, which in 

 the experiments was such as to increase osmotic pressures 

 from four or five to ten or twelve atmospheres, might retard 

 evaporation from the cell-membranes. (2) A diminution of 

 the degree of succulence, or proportion of water per unit area 

 of surface present, might lessen transpiration. (3) Desicca- 

 tion may result in alterations in the character of the outer 

 membranes or of any of the transpiring cell-walls of the 

 plant. (4) Desiccation may stimulate the formation of new 

 tissues or the alteration of existing cells in such a manner as 

 to close openings through which water-vapour might pass. 

 (5) The positions of the surfaces might be shifted in such 

 manner as to vary the exposure and lessen transpiration. 



With regard to (1), however, Livingston has shown that 

 concentration of the sap, even if carried to a point where an 

 osmotic pressure of one hundred atmospheres was attained, 

 would not result in a retardation of more than ten per cent, 

 in the rate of evaporation from a free water-surface ; hence 

 this factor is negligible in the present case, as the increases 

 found were not more than five or six atmospheres. 



RESISTANCE OF PLANTS TO FREEZING.— In the 

 New Phytologist, Vol. VIII (1909), under the title "Vegeta- 

 tion and Frost," Dr. F. F. Blackman gave an interesting 

 summary of this subject, drawn from the researches of Miiller, 



Molisch, Mez, Gorke, and Lidforss. Miiller and Molisch held 

 that the fatal effect of freezing upon plant-cells is due to the 

 withdrawal of water from the protoplasm ; but the work of 

 Mez went against this view. Gorke investigated the changes 

 in composition produced by freezing either entire plants or 

 their pressed-out sap, and showed that when water was with- 

 drawn from the cell by freezing, the salts present became 

 more concentrated and eventually caused the precipitation of 

 the soluble proteins of the cell. Lidforss found that " winter- 

 green " plants — delicate herbaceous plants which still bear 

 green leaves in mid-winter, though showing no obvious 

 structural adaptation for protection against cold — contain 

 quantities of sugar in winter, this being replaced in summer 

 (or in winter if the plants are brought into a warm room) by 

 starch ; and his observations strongly support the view that 

 the presence of sugar retards the "salting-out" or precipitation 

 of the proteins, which Gorke had described. 



The chemical means of protection of plants against freezing 

 have recently been investigated by Maximow (Ber. deutsch. 

 bot. Ges., 1912). He finds that the introduction of neutral 

 organic substances, such as carbohydrates, alcohols, and 

 acetone, into the cells of plants increases their power of 

 resisting cold, in the case of tropical plants as well as those 

 of temperate climates. The protective action of such sub- 

 stances does not stand in direct relation to the osmotic 

 pressure and the lowering of the freezing-point — as the con- 

 centration of the substance rises, the resistance to cold 

 increases at a more rapid rate than the lowering of the freezing 

 temperature. Different substances differ in their effect, and 

 of the substances tried the sugars have the greatest effect ; 

 then come glycerine, the alcohols and acetone. On the with- 

 drawal from the cells of the protective substance which has 

 been artificially introduced into them, the power of cold- 

 resistance returns to its original condition ; and when " winter- 

 green " and other plants are placed for some time in water, 

 their cold-resisting capacity is diminished. 



CHEMISTRY. 



By C. Ainsworth Mitchell, B.A. (Oxon), F.I.C. 



THE MANUFACTURE OF SUGAR FROM SAW- 

 DUST. — In a recent issue of the Journ. Roy. Soc. Arts 

 (1912, LXI, 69) there is an interesting outline by Mr. A. 

 Zimmermann, of the manufacture and utilisation of the sugar 

 produced by hydrolysing sawdust with an acid. The methods 

 employed in obtaining alcohol from woody fibre have already- 

 been described in these columns and the Classen process used 

 in the production of the new commercial product " sacchu- 

 lose " is based upon similar principles. The sawdust is 

 treated with a solution of sulphurous acid in a closed vessel 

 under a pressure of ninety to one hundred pounds per square 

 inch, with the result that a product containing about twenty- 

 five per cent, of sugars and a porous friable residue of modified 

 wood fibre is obtained. 



Owing to the changes in the physical and chemical structure 

 of the material the crude product will readily oxidise on 

 exposure to the air, and to obviate this the " sacchulose " is 

 mixed immediately after its formation with a certain propor- 

 tion of molasses or fatty matter, with the object of preventing 

 the air from coming into contact with the sugars. 



Experiments upon the use of the mixture as a feeding stuff for 

 animals have given very good results. The trials were made 

 upon working horses and extended over a period of six 

 months, four lbs. of the oats in their former daily rations 

 being replaced by four lbs. of the prepared " sacchulose." 

 At first the animals lost in weight, but after they had become 

 accustomed to the change, increases in weight of thirty to 

 eighty lbs. were recorded. 



Eighty per cent, of the sugars are fermentable and the 

 original idea of the manufacturers was to produce a cheap 

 commercial spirit which might possibly be used as a fuel for 

 motors. The spirit obtained by fermentation and distillation 

 of the soluble sugars is of excellent quality, and acetic acid, 



