halls. The vascular hundk-s showed the well-known frost hrowninj;-. The 

 fact that exactly the midline of the intercostal helds is always the part 

 injured by frost is explained hy the peculiar folding of the leaf surfaces 

 in the bud primordia. 



1 found the same phenoniena also in .leer PsciiJoplatinius and some 

 other thick-leaved varieties of maple; in these, however, only in the form 

 of irregular i)erforations. l.aubert' observed a feathery slitting of the 

 leaves of the birch and the white beech. Thomas- explains the slit condi- 

 tion of the leaves chiefly as a result of the action of the wind. It has been 

 known, e\er since A. Braun and Caspary, that chestnut leaves can be per- 

 forated and in places slit by the mutual rubbing of the leaf surfaces, but 

 the ])henonienon here described has nothing to do with the action of the 

 wind. 1 lia\e found the beginnings of the sjjlit leaf condition in little trees 

 which had been brought into the house soon after the action of the frost'''. 



Thf. Hi:.\viNr, of Seeds. 



Aside from the injuries which hardy herbaceous plants can suffer from 

 lying too long under a snow cover, because they are often suiYocated, we 

 have to take into consideration another phenomenon which becomes espe- 

 cially disadvantageous for grains, i. e.. the heaving of young plants. 



It is onlv the soils which contain a great deal of water which exhibit 

 the heaving of seed by frost. After unsettled winter weather, when sharp 

 frosts suddenly follow wet days in the early spring, a number of young 

 plants with exposed roots are not infrecfuently found on the upper surface 

 of the field. A part of the roots, to be sure, still touch the earth with their 

 tips, and eke out for the seedlings a pitiful existence, while other rootlets, 

 jjerfectly free, with torn tips, are exposed to drying wind and sun. The 

 explanation of this occurrence is \ery pertinent here. The heavy soil 

 retains large tjuantities of water; this freezes into long, needle-like crystals 

 and thereby raises the ui)per layers of the soil, together with the young seed, 

 if a part of the hue roots ha\e alread\- reached a considerable depth they 

 are torn loose. In the subsequent thawing the soil can settle back in place, 

 but not so the young plants. A repetition of the process finally brings the 

 above result and may cause consideral)le loss if help is not brought quickly. 

 The help consists mainly in the use of a heavy roller at a time when the 

 soil has already dried to some extent. P)y pressing the sprouted seed, the 

 lower nodes of the stem obtain protection and dampness enough to put out 

 new adventitious roots and in this way gradually overcome the injury to 

 the organs which hold them fast and nourish them, h'.specially in grain 

 plants rolling acts beneficially and in damp si)ring weather strong blades 

 will grow from plants which ha\ e thus been drawn out of the soil. 



1 Laubert, R. Resel\viclri.i;o Ka.stenienlilatlPi-. fJartenflora, '>2. .lahrg-., 1903, 

 Ol<toher. 



■- Thomas, Fr. Die meteorologischen Ursachen der Schlitzt)liitteriskc'it von 

 Aesculus Hippocastanum, Mitt. d. Thuring. Bot. Vor. I!t04, fait liJ, p. 10. 



•: ri. Z. f. I'llanzinkrankh. 1905, p. 234, Note. 



