386 



SCIENCE 



[Vol. LV, No. 1424 



the water held by eolloids possesses properties 

 different from those of "free watei'," particu- 

 larly with regard to the temperature at which 

 it freezes. This work suggested to Bouyoucos 

 of the Jlichigau Agricultural College a classi- 

 fication of soil water into "free" water, which 

 freezes at 0° C. or slightly below, eolloidally 

 adsorbed water which freezes at temperatures 

 from a few degrees laelow zero down to -7S°C., 

 and combined water, which freezes only at 

 temperatures below -78°C. This classification 

 was applied by McCool and Millar to the water 

 of plant tissues. The work of these investigat- 

 ors suggested an explanation of the gi'eater 

 tenderness of plant tissue with the higher water 

 content. If hardiness depended not on the 

 total water content, but on the content of eol- 

 loidally adsorbed water which does not freeze 

 at ordinary freezing temperatures, then a plant 

 tissue might contain any amount of free water 

 and still be tender, while a relatively small 

 amount of water in the adsorbed condition 

 would impart a considerable degree of hardi- 

 ness. Recent investigations at the Universit5f 

 of Missouri have shown that these surmises 

 are correct, at least for some plants. 



If hardiness depends on the amount of eol- 

 loidally adsorbed water, what colloid holds it 

 in this adsorbed state? Some botanical in- 

 vestigations by Spoehr of the Carnegie Institute 

 suggested the probable answer to this question. 

 He found that in cacti water-retaining capacity 

 is correlated with pentosan content and that 

 when the water-retaining capacity is increased 

 or decreased by changes in environmental con- 

 ditions, the pentosan content likewise increases 

 or decreases at the same time. Pentosans were 

 therefore investigated in fruit plants and vege- 

 tables and a correlation was found between 

 pentosan content and hardiness. This corre- 

 lation is remarkably close if hot water soluble 

 pentosans only are considered. These findings 

 indicate that certain pentosans, probably pec- 

 tin-like substances, are the colloids that hold 

 water in an adsorbed state. This is further 

 substantiated by the fact recorded by Spoehr 

 that dryness tends to increase the pentosan 

 content of cacti and likewise their water re- 

 taining capacity. It is well known that cul- 



tural practices or climatic conditions that tend 

 to dry fruit plants out in the fall, increase 

 maturity and hardiness. Consequently the very 

 conditions that lead to a low total moisture 

 content probably increase the amount of water- 

 holding eolloids and the quantity of eolloidally 

 adsorbed water — hence the greater hardiness of 

 plant tissues with the lower moisture content. 



This understanding of the conditions asso- 

 ciated with hardiness in plant tissues permits 

 accurate outlining of the treatment or treat- 

 ments that decrease susceptibility to low tem- 

 peratures. It makes possible also an estimate 

 of the magnitude of the effects that may be 

 produced in that direction, and a recognition 

 of their limitations. Such practices thus be- 

 come incorporated in scientific horticulture. 



This example indicates the intimate i-elation 

 between progress in horticulture and progress 

 in other sciences. Subjects which on super- 

 ficial consideration might never be suspected of 

 contributing data valuable for the solution of 

 horticultural problems are seen to be worthy of 

 studj". If little headway has been made along 

 certain paths of investigation, it is not infre- 

 quently because the methods, the facts or the 

 technique essential to the solution of specific 

 problems has been lacking. To this day, the 

 ofiicial method for the determination of starch 

 recommended by the Association of Official 

 Agricultural Chemists is not an analysis for 

 starch but for total hydrolyzable polysaccha- 

 rides. Furthermore it is onlj within a com- 

 paratively few years that a satisfactory 

 method for determining total sulphur content 

 has been available. As a result, much pains- 

 taking labor has gone for naught, though some 

 have noted, but have been at a loss to account 

 for, the discrepancy between the results of 

 such determinations and the unmistakable evi- 

 dence of microchemieal findings. The investi- 

 gator can well afford to acquaint himself with 

 recent advances in other fields and the broader 

 his fund of information the more successful he 

 will be. It might be suggested that progress 

 in Physics, Meteorology and Forestry should 

 be watched as well as that in various branches 

 of Botany, in Chemistry, Soil Science and 

 Agronomy. This task which would have been 



