PERIODICAL LITERATURK 



P.()TAXV AND Z()()L()(;V 



As late as December 1. 1!»1!), many tree species 

 l.atr Retention -till liad all or some of their leaves. The jjear 

 oi foliage in the {Pirns coniuiniiis) . Red thorn {Crataegus man- 

 fall of igig O(iyna). the garden rose, blackberry (RHbus 

 easins), and peach {Pruniis pcrsica) had shed 

 only a little of their foliage. The exi)lanation of this phenomena rests 

 on a review of al! the meteorological conditions through the year. The 

 temperature, due to a late and cold sj^ring. was such that the vegetative 

 period was prolonged, m order to enable the trees to produce the 

 normal amount of storage energy and material for the winter. A 

 cool summer further held back the vegetative activity. Meagre pre- 

 cipitation in May, July and September had its influence in curtailing 

 the vegetative energy. Heavy precipitation in October encouraged the 

 growth to make up for delayed summer growth. At the beginning of 

 November, the trees had not yei arrived at the condition which wcuM 

 allow a passing over into the period of vegetative rest. In other words, 

 the formation of the layer of parenchymatous cells at the base of the 

 petioles which enables the leaf to fall away easily from the stem had 

 not been formeil in many tree species. With the beginning of No- 

 vember came heavy snows and continued cold weather which inter- 

 rupted growth and hindered the formation of the parenchymatous 

 layer. The trees were forced into their rest period, the leaves 

 gradually cea^ed their activities, and very slowly died and dropped ofr. 

 Summing up. a combination of adverse conditions — a late spring, a 

 cool suyimer, a wet October, and an early November frost — wa> re- 

 sponsible for the rather extraordinary retention of the foliage in the 

 fall of 1919. J. RoKsi-R. 



Pietsch, Albert. W'ic erkldrt sich das langc Hdngenbleiben der Blatter an 

 einigen phancrogamcn Holzgeu'dchsen im Herbste 1919. Xaturwiss. Zeitzchr. 

 Forst- u. Latidwi. 18:150-15.o. 1920. 



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