532 



out from- frozen cahbajre plaiit^^ wliilc llic same [)ressure ga\e only 7.1 per 

 cent, sap in examples which had not l)een frozen. 100 com. of sap con- 

 tained in 



frozen plants not frozen [)lants 



Dry substance 7.96 'fH; 4.04 g 



]\a\\ Ash ' 1.63 " 0.97 " 



( irape Sugar 4-1/ " 1.41 " 



1 )extrin ( ?) 0.80 " 0.58 " 



Nitrogenous substances 0.80 " 0.51 " 



l'^xtracti\e substances free from nitrogen 0.50 " 0.54 " 



This shows that the soluble elements in the sap have undergone a con- 

 siderable increase and that, in this, grape sugar is especially concerned. 

 Here, therefore, just as great a formation of sugar has been found as in 

 the potato; .Schmidt' states this to be 21.85 per cent. 



Frost I'li.stf.ks. 



Frost bHsters are of less significance agriculturally but certainly worthy 

 of consideration scientifically because of the ])roduction of mechanical dis- 

 turbances in the tissues inside the organs which remain ali\e. These mani- 

 fest themseKes in the ai)i)earancc of usually small, blister-like places in the 

 epidermis and at times also in the suli-epidermal layers which are raised 

 from the thin-walled i)arenchyma of the leaf flesh or the tougher [)aren- 

 chyma ot the leaf \eins. Instead of an extensi\e descvij)tion. we will 

 reproduce in I'ig. 107 a cross-section- of the frost blister on an api>le leaf. 

 O indicates the upper side, U, the under side. M is the mid-rib. .v a larger 

 lateral veiri. 



In the r!ii(l-rib. the crescent-like wood bod_\', with its numerous ducts 

 ((/), forms the chief part. On the upper side adjoins a thin walled layer 

 of parenchyma (in) free from chlorophyll. corres[)onding to the pith body 

 of the axis. This parenchyma layer is co\ered by thick-walled collen- 

 chymatous cells (c) ; these dexelo]) more abundantly, the larger the \ein is. 

 The collenchyma extends as firm wedges somewhat abo\e the part of the 

 leaf surface which consists only of leaf flesh. The leaf flesh shows the 

 usual di\ision into palisade parenchyma (p) and spongy parenchyma (sp). 

 Of these layers, containing chloroplnll, the palisade parenchyma does not 

 extend over the \ascular bundles on the upper side but spreads out on both 

 sides like a keel so that it terminates in a short cell layer (br). This be- 

 comes one layered, between the collenchyma and the parenchyma of the 

 body of the ^ein. The spongy parenchyma, on the other hand, extends on 

 the under side over the body of the vascular bundle and forms the bark part 

 of the vein in which, as in the l)ark of the branch, may be found oxalate 

 crystals (0) arranged in crescent-like rows. The e])idermis (c) covers 

 the whole leaf uniforml}. 



1 After Ritthau.sen; cf. "Dor l^aiulwirt" 1875, j). .501. 



- Sorauer, P. I-'rostblasen an Blattein. Z. f. I'Hanzeiikrankh. 1U02, p. 44. 



