IM BOTANY OF THE LIVING PLANT 



Howerin [uently tends to be arreted in plants growing in 



inip l, in honeysuckle and other plants growing 



r . though some plants flower freely in such 



Th , , Kperiments of Klebs in this field of m- 



him to the belief that {lowering is favoured by a 



rbohydrates within the tissues, especially in 



mparison with nitrogenous substances. Defective light will tend, 



t on photosynthesis, to prevent this condition. An 



t nitrogenous manure will also have the same result, and it 



h | uently been observed to lead to vigorous vegetative growth, 



Dut , production. In the presence of abundant reserve food 



; may, however, occur in darkness, as in the case of some 



bulbou- plants. 



The length of daily illumination is also an important factor in 

 termining the time of flower formation under natural conditions: 

 artificially adjusting this the time of flowering can in some cases 

 ►ntrolled, though a number of plants are relatively insensitive 

 to day-length. In <ome plants, of the so-called short-day type, flower- 

 ing , hastened by exposure to artificially shortened days. 

 samples are Dahlias, Chrysanthemums, and the Runner Bean. 

 - ich plants tend in these latitudes to produce their flowers in the 

 shorter days of autumn: but by exposing Dahlias to shortened days 

 from the time they were planted, flowering has been secured in July 

 instead of September. In long-day plants flowering can be hastened 

 by exposure to lengthened days, using artificial light for the purpose- 

 • lis .ire examples of this type, and they normally produce their 

 flowers in the summer months. Exposure of these plants to shortened 

 da ' nds to suppress flowering. These effects of the length of daily 

 illumination are not yet understood, but they have considerable 

 practical importance : thus in introducing a new crop into a particular 

 m, the influence of length of day upon flowering and fruiting 

 must be considered, and those varieties selected which are best fitted 

 local conditions in this respect. 



•arc may also affect reproduction. It has been found that exposure 

 of a plant to low temperature during germination may hasten the onset of 

 flowering. This has Ken applied practically, and is described as vernalisation. 

 A Miml seen m biennials, such as the turnip, which tends to flower 



in the tirbt year if exposed to frost. 



4. Periodicity in Growth. 



The plant exhib'ts frequent changes in its growth activities. Thus during 

 the course of the yearly growth -season the phase of vegetative activity is 



