^8 THE FACTORS [Part I 



The category of functions tliat arc active at loiv temperatiues only 

 includes among others the obscure processes which are fermentative in 

 nature, according to Sachs' hypothesis, and which awaken into activity 

 hibernating parts of plants ; among such processes may be cited the 

 conversion of starch into fatty oil and the reverse. The chapter on Periodic 

 Phenomena in Temperate Regions will include a full account of what is 

 known in regard to this subject. Erikson has shown that, in like manner, 

 the germinating power of certain fungus-spores is markedly increased by 

 cooling them down nearly to zero ; according to F. Haberlandt, a similar 

 result follows on cooling down swollen flax-seeds for several days. 



Certain movements due to stimuli, such as those of the chlorophj'U- 

 corpuscles, are arrested by low temperatures. The needles of certain species 

 of Pinus at a low temperature become adpressed to the axes. Many sub- 

 stances are produced during cold weather ; for example, the red drops 

 of oil that cause the brown winter-colour of many conifers. The list of the 

 functions of plants that are called into action at low temperatures only 

 could yet be considerably increased. But only one more of them will 

 be mentioned here, on account of its great importance in geographical 

 botany. 



Low temperatures jMrLa favourable influence onjhe sextialorgcuis and on 

 the parts oecologically connected with them (perianths, inflorescence-axes) 

 /// many plants of the temperate and frigid zones. The cardinal degrees 

 for the growth — and perhaps for the inception — of the primordia of flowers 

 are often much lower than for the growth of vegetative shoots, so that the 

 former are favoured by a relatively lower temperature, and the latter 

 by a higher temperature, during development. It is well known that 

 Crocus, Hyacinthus, and other perennial herbs do not send out flowers 

 or inflorescences at a high temperature, but shoot out luxuriantly into leaf 

 Also in the forcing of fruit-trees the temperature must be kept moderate] 

 before, and especially during, the blossoming period. For the same reason 

 many temperate plants seldom blossom in the tropics ; for example, most of 

 our fruit-trees. Fritz Mliller observed at Blumenau that various European 

 herbs never, or hardly ever, blossomed ; amongst them were Carum Carui, 

 cabbage, turnips, parsley, and celery. Echium vulgare blossomed in his 

 garden only once after an exceptionally cold winter. Kurz found in the 

 mountains of Burmah that increased coolness due to increased altitude 

 expedited the blossoming of temperate plants such as Rhododendron and 

 Gentiana, but delayed that of tropical ones. It has been already stated 

 that seaweeds fructify during winter in the arctic seas. Several other 

 isolated observations of the kind might be cited. Consistent, thorough, 

 and cornprehensive research is, however, altogether wanting on this question, 

 which is extremely important in geographical botany. 



I 



