Killing of Plant Tissue by Low Temperature 



179 



While the dififerences are not large, it will be seen that the sap 

 density of the shaded plants is uniformly lower and the killing 

 greater. 



Ohlweiler^ at the Missouri Botanical Garden seemed to find some 

 relation between the density of the sap of different plant species and 

 their resistance to cold. This is true especially in the case of the 

 different species of magnolia, where the leaf structure of species 

 with dense sap and of those with dilute sap is similar, so there 

 would not be this influence involved to modify the results. 



From the beginning of these experiments, observations have 

 been made in autumn as to plants killed by the various early frosts 

 and freezing point determinations were made from leaves of these to 

 see if there is to be found any relation between hardiness and sap 

 density. In the following table the plants are listed as nearly as 

 could be determined according to hardiness, the most tender first, 

 though it is certain that almost any of the plants could be changed 

 two or three places in the succession and be as accurately placed in 

 order of hardiness. The depressions are also given. The leaves for 

 the depressions were all taken in the morning as soon as the dew was 

 off so they would be equally turgid. 



Table 11. Showing the Relative Hardiness of Growing Plants 

 Compared With Their Relative Sap Density. 



Plant 



Morning-Glory (Ipomoea purpurea) 



Coleus (C. Blumei) 



Sweet Potato (Ipomoea Batatas) 



Moon Vine (Ipomoea Bona-Nox) 



Watermelon (Citrullus vulgaris) 



Cantaloupe (Cucumis Melo) 



Cucumber (Cucumis sativus) 



Caladium (Colocasia antiquorum) 



Pumpkin (Cucurbita Pepo) 



Tomato (Lycopersicum esculentum) 



Lantana (L. Camara) 



Dahlia (Dahlia variabilis) 



Blue Salvia (Salvia patens) 



Red Salvia (Salvia splendens) 



Rose Geranium (Pelargonium graveolens) 



(jcranium f F'elargonium Hortorum) 



Eggplant (Solanum Melongcna) 



Alternanthera (Telanthcra versicolor) 



Periwinkle ( Vinca major) 



Ageratum (A. conyzoides) 



Chard (Beta vulgaris var. Cycla) 



Celery (Apium graveolens) 



'23d. Aiil. Kpt. Mo. Hot. Card. 1912, pi). lOI-.U. (Ull)!. H7) 



