upon the depth to which the seeds are covered. It seems desirable to have 

 this still less tlYkn for grain (0.5 to 2.(5 cm.). Wollny's experiments showed 

 that in dry years a deeper earth covering was more advantageous, in wet 

 years, a lighter one. Corresponding to wet and dry weather the time of har- 

 \ est w^as retarded with an increasing depth of sowing, the number of plants, 

 which germinated at all and still more, the number which came to harvest, was 

 decreased. But it must be emphasized again and again that precise figures 

 for the most favorable sowing in the different localities can be collected only 

 directly by the local' agriculturalist since not only the composition of the 

 soil and the weather but also the character of the variety must be con- 

 sidered in the matter, as has been shown by Stossner\ 



This same holds good for tubers, bulbs and pieces of roots which are 

 used for seeds. In these the soil conditions have an especial weight because 

 these fleshy organs which are rich in water are essentially and quickly in- 

 fluenced by the soil supply of oxygen . For potatoes, experiments by 

 Nobbe- and Kiihn' have shown that in questionable cases the more 

 shallow sowing wall be the most advantageous one. In the forcing of bloom- 

 ing bulbs excessive losses arise at times from the fact that the bulbs (hya- 

 cinths) have been planted too deep in the pot, or when in the pots are cover- 

 ed too deep with earth after the rooting has been sufficient. Especially if the 

 soil covering is heavy and damp and the bulbs have not matured sufficiently 

 the year before on account of wet weather, the "Rotz" (see this in A^ol. IT.) 

 usually appears very easily. 



The automatic regulation of the depth of sowing on the part of dift'erent 

 plant races is interesting. In grasses, and in fact, best seen in our grain 

 species, the first internode is the part which is destined, when the seed grain 

 has been sown too deep, to push the second node which hides the stem eye 

 and the side buds, i. e. the node which forms the stem, into the porous, well 

 ventilated upper layer of soil. In the adjoining figure 9 we perceive the 

 seed grain which is already almost empty and its weakly retained (primary) 

 roots which had been formed in the grain. From the seed grain the first 

 (over-elongated) internode has pushed the second node nearly up to the 

 upper surface of the soil. In this favorable position the secondary roots, 

 which exist during the whole life of the plant, have been developed, the eyes 

 of the side shoots have attained a further maturity. In shallow sowing both 

 nodes lie close to one another and give in cross-section such a picture as is 

 shown in figure 10. The nodal tissue seems divided radially by browned vascu- 

 lar strands. The vascular-bundle cylinders are those of the primary roots and 

 become diseased during or soon after the formation of the secondary roots. 

 The ground tissue of the node shows the first circle of vascular bundles fg) 

 of the young blade close to the pith shield fin ) with its' few cells. Branches 

 of these bundles, recognizable from their wide ducts (g), may be seen fur- 



1 Stossner, l^ntersuchungen liber den Einflu.s§ verschiedener Aussaattiefen et< 

 Landwirtsch. Jahrbiicher ISSi. 



- Nobbe, Handbuch der Samenkunde, 1876, p. 184. 



3 Kiihn, Berichte aus dem physiolog. Laborat. Halle, Part I., p. 43. 



