io6 



In ftlantlng streets, besides the embankment which sometimes becomes 

 necessary, the asphaltincj and cementing of the street causeways is also very 

 injurious to the roots of the trees. The injury is due not only to the shutting 

 off of the atmospheric air but also the loss of precipitation from the air, upon 

 which trees in large cities become so much more dependent, as the level of 

 the ground water has fallen because of canalization and the workings of the 

 subsoil in building. Young trees which are planted after the falling of the 

 level of the ground ivatcr strive to reach this despite the increased depth of 

 the springs. Consequently in order to facilitate this, the holes for planting 

 the trees must be made considerably deeper in such localities. According to 

 Bouche, this increased depth amounts to 60 cm. in Berlin so that now the 

 holes for planting trees must be dug i. 5 cm. deep. 



Too Deep Sowing of the Seed. 



The discovery has also often been made that from a plentiful sowing 

 of good fresh seed a comparatively small number of plants is produced. As 

 is generally believed, the cause lies more frequently in sowing the seeds too 

 deep. When harrowed in or hoed under in places, as is customary with 

 barley\ some seed grains necessarily come to lie too deep, others 

 too superficially. Uniformity can be obtained only by planting with a drill. 

 But even the gardener, who can cover his seeds very uniformly in seed pans, 

 not infrequently obtains only a low- percentage of plants in sowing very fine 

 seeds even if the seed was good and of high germinating quality. 



The processes causing the loss, however, are not always the same, and 

 do not always take place under the same conditions ; on this account it is 

 impossible to generalize. In order to protect oneself from injury in this 

 connection, there is nothing to be done except to understand clearly the in- 

 fluence of the different factors to be observed in sowing seed and to see 

 which combinations exist in every individual case. 



There are three phases in germination. Each can be disturbed and 

 cause failure. The first stage consists of the swelling of the seed and is a 

 mechanical process, in which (probably by water condensation) an increase 

 in temperature has been observed. This introduces the second stage, the 

 mobilisation of the reserve substances, a chain of chemical phenomena, and 

 these accompany the third act, that of the formal development. 



Disturbances in the stage of swelling have often been observed. Nobbe 

 and Haenlein- found especially in Papilionaceae and Caesalpiniacea, 

 that the seed shell at times is so hard that water can not enter, that the seeds 

 retained the embryo for years without development, but always in a healthy 

 condition. The seed did not germinate because it did not swell. In clover 

 seed, the superficial shell or hard layer containing the coloring matter, is 



1 Eggers-Gorow, Versuche iiber den Nutzen oder Nachteil einer flachen oder 

 tiefen Bestellung- der Gerstenkorner. Meoklenb, landw, Ann, 1874, No. 23. 



- Nobbe und Haenlein, Ueber die Resistenz von Samen .2:egen die aufseren 

 Faktoren der Keimung. Versuchsstationen 1877, p. 71. 



