May, 1921. 



SCIENTIFIC AGRICULTURE 



211 



assimilation is liiiidered. If the soil during mid-sum- 

 mer is dry in the upper layers so that nitrifieation is 

 impeded and the sujjply of nitrogen thereby decreased, 

 tJie plant then obtains a larger supply of carbohydrates. 

 The shoots are thus forced, as a result of a smaller sup- 

 ply of nitrogen to conclude their growth earlier in the 

 summer and are- therefore able to mature at a time when 

 the days are longer and the tem])erature more favour- 

 able for carbonic acid assimilation wliereby the cells be- 

 come more abundantly provided with stored-up mat- 

 erial. A sunnj- and warm summer which at the same 

 time is dry, is therefore one which induces greater winter 

 liardiness in trees and shrubs. The different elements 

 of plant food in the cell have consequently a great in- 

 fluence on the degree to which trees and shrubs may be 

 able to withstand frost. An abundant supply of nitro- 

 gen results in the shoots .starting early and growing late 

 in the summer. Their cells become comparatively large, 

 thin-walled and poorly supplied with stored-up mat- 

 erial both soluble and insoluble. Such shoots are dam- 

 aged very easily by a tolerably liglit frost. Plants must 

 on the other hand be furnished with a good supply of 

 potash in order to be able to reach the highest degree 

 of winter hardiness. Where potash is deficient in the 

 soil the assimilation of carbonic acid is impeded, the 

 supply of carbohydrates is less and the cells become 

 poorly supplied with stored-up material, and as a re- 

 sult are less hardy. The lack of potash may also in- 

 fluence hardiness in plants by arresting the assimilation 

 of carbonic acid causing the general development of the 

 individual to be delayed so that the shoots do not mat- 

 ure until late in the summer, when less carbohydrate 

 can be prepared for storing up in the cells. A similar 

 effect can take place through the lack of phosphoric 

 acid. A good supply of potash and phosphoric acid con- 

 sequently is a necessary condition in order that trees 

 and bushes may be able to reach the highest possible 

 degree of hardiness." 



The manner in which the season may influence both 

 the hardiness of a plant and the production of flowers 

 and fruit in the following spring was shown in Middle 

 Sweden in the years 1901-1902. The summer of 1901 

 in this region was uncommonly sunny, warm and dry, 

 while 1002, according to reports, was quite the opposite, 

 even to a marked degree. During the summer of 1902 

 it was found that a White Mulberry tree (Morus alba) 

 growing in the Botanical Garden at Uppsala and which 

 ordinarily is very susceptible to cold and frost, had 

 withstood the winter almost perfectly. It produced an 

 extraordinary abundance of flowers and berries during 

 this summer — something which almost never before 

 had been recorded in a latitude so far north. The sum- 

 mer of 1902 however, was very rainy, cold and sunless, 

 as a result of which this plant became poorly equipped 

 to with,stand the winter and was very severly injured 

 thereby, although this winter was not especially severe. 



"The extra hardiness of the ("ambinm and other ad- 

 joining layers depends partly on tlie high osmotic pres- 

 sure wiiich exists in these layers and which is necessary 

 as a protection against the pressure which the surround- 

 ing bark exercises, and partly because of the fact that 

 the young cells are filled with protopla.sm. As a result 

 of the hitter condition the concentration of the cell con- 

 tent, which is always increased by freezing, becomes es- 

 pecially intense." 



Hardiness in autumn-sown Wheat. 



At the Plant Breeding Station at Svalof, Sweden, 

 the question of hardiness in autumn wheat has been 



very carefully studied for many years. This study has 

 been greatly facilitated by the pedigree or separate cult- 

 ure system which has been practiced at that institution 

 for twenty-five years. Since each of these cultures con- 

 sists of the progeny of single plants, it is possible to 

 obtain exact data as to the relative attitudes of the dif- 

 ferent .strains or biotypes towards frost. These invest- 

 igations showed, among other things, that each strain 

 has its own peculiar degree of hardiness which is trans- 

 mitted in quite the same way as are other qualities. It 

 was also shown that the frosts of midwinter may, under 

 certain conditions, be more dangerous than is the freez- 

 ing and thawing of .spring, although the latter is usually 

 believed to be more destructive. 



It has Ijeen shown at Svalof that one of the first es- 

 sentials for frost resistance in autumn wheat is a well 

 developed plant, it having repeatedly been ob.served that 

 the roughest and best developed plants are best able to 

 withstand the severe conditions of winter and early 

 spring. It has also been a matter of common observa- 

 tion that jilants from small poorly developed seed do not 

 stand the winter so well as a rule, as do those plants 

 which have come from seed which is large and plump. 



Where the stand of autumn wheat is excessively thick 

 experience has shown that there is a decrease iri hardi- 

 ness. This is accounted for by the fact that in the ease 

 of a thick stand a smaller number of shoots are deve- 

 loped from each seed and these grow long and are poorer 

 in texture. Since thick stand is influenced bv soil and 

 seasonal conditions as well as by the variety which is 

 used, it is advised that sorts which are likely to stool 

 heavily be not .sown too thickly. 



In 1899 frost did its worst damage to the autumn 

 wheat crops at Svalof in the spring, while in 1901 the 

 greatest damage was wrought in January. In the.se 

 cases the drying out of the shoots above 'ground may 

 have been the immediate cause of the death of the plant 

 It IS believed in fact that the 'hardiness' of a sort de- 

 pends in a large mea.sure upon its ability, bv virtue of 

 Its inner and outer structure, to withstand flri/iiuj. 



The root system of the plant, judging from observa- 

 tions at Svalof. also seems to play an important part in 

 determining the degree of damage done by frost. Xo 

 relation wa.s .shown to exist however between density of 

 head, character of chaff, absence or presence of awns 

 and hardiness. 



Acclimitization of Wheat. 



Tiic matter of acclimitization in pure lines (biotypes) 

 of wheat, while immensely important from a practical 

 standpoint, is of great interest to the scientist in the ex- 

 tent to which it directly effects the question as to 

 whether or not hereditary changes can ari.se from rjra- 

 dual alterations in the character and structm-e of the 

 type. 



Investigations which have been conducted in Scandi- 

 navia and elsewhere seem to show that if f/rxuhir aceli- 

 mitizati'm exi.sts. it may be regarded as a manifestation 

 of the inherent power of the organism to directly adapt 

 itself to its conditions. Gains in hardiness which have 

 been recorded in the case of such cross-fertilizinsr plants 

 as Alfalfa and Maize cannot be regarded as acelimitiza- 

 tion in its strictest sense, since in these cases the hardier 

 forms presumably consist of combinations of characters 

 which have been effected by cross-fertilization and which 

 have proven more hardy than either of the parents. 



An instance .showing how hardier forms niav be pro- 

 duced as a result of crossing sorts of intermediate hard- 



