639 



longer the plant is left in a condition of rigor, the more slowly can it take 

 up its activity again^. We will become acquainted with other main points 

 on the subject of difference in susceptibility in the following actual occur- 

 rences. 



Poor Development of Our Vegetables in the Tropics. 



When cultivated plants from the temperate zones are carried to tropical 

 regions very great disturbances become noticeable at times in the ontogeny 

 of the plants, which severely impair the cultural aim. This lies in the unde- 

 sired abbreviation of the different phases of growth, especially in the 

 shortening of the period of leaf development, and of the production of 

 reserve substances which are used up too early for the development of the 

 reproductive apparatus. This is especially marked in the case of plants in 

 which the period of growth has been prolonged by continued cultivation in 

 soil abounding in nutritive substances, i. e., rich in nitrogen, and the leaf 

 apparatus has been developed luxuriantly (varieties of cabbage, lettuce, 

 etc.). We find cases of this nature reported in older works. Thus, for 

 example, Duthie cites such a case from Saharanpur-. His experiments in 

 India on plant structures show, with a few exceptions, a too rapid ripening 

 of the seeds of European plants. While the beet {Beta vulgaris var. rapa) 

 takes i8 months in England to complete its development, it needs in India 

 only 8 months. In the cultivated forms of German asters, the effect of a 

 change of climate manifests itself in the non-ripening of the seed. The 

 blossoms of Brachycome and Petunia change and all become white. The 

 process seems to me to represent the opposite of the process of the redden- 

 ing of plant parts in spring, due to a lack of heat. 



Similar phenomena have been reported from tropical America. Leh- 

 man' found in Western Colombia that cabbage, lettuce, onions and carrots 

 did not develop sufficiently for cultural purposes. While seeds, imported 

 from Europe, furnish in the first year, in-corresponding localities, excellent, 

 tender vegetables with a desired amount of development, seeds from these 

 individuals give ])lants which, in cabbage and lettuce, show only traces of 

 head formation while the onions grow out into stalks a finger thick without 

 any tenderness, or flavor. The plants here have no dormant period. 



In the level equatorial regions this phenomenon occurs sooner and 

 more noticeably than in the higher, mountainous regions and between the 

 loth to 15th parallels of latitude.. 



Postponement of the Usual Seed Time in Our Latitudes. 



We must here consider the phenomenon, not infrequently observed, 

 that vegetables, sown too late in the year, come into the hot, dry season too 



1 Hillirig-, H., iJber den Einfluss supramaximaler Temperatur auf das Wachstum 

 der Pflanzen. Inauguraldissertation. I^eipzig- 1900; cit. Just, Bot. Jahresber, 1901, 

 II, p. 203. 



2 Gardener's Chronicle 1881, I, p. 627. 



3 Lehmann, Uber eine physiologische Erscheinung bei der Gemiisekultur im 

 tropischen Amerika. Deutsche Gartnerzeitung 1883, p. 260. 



