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FLOWERING PLANTS 



BY LIGHT CONTROL 



More economical production in the greenhouse has become possible as 

 'growers have increased means of control over plant growth. There is much 

 still to be learned and,- once learned, applied to commercial culture. Here 

 is a means of control which m^y before long he attempted. 



HAT there exists an in- 

 timate relation between 

 the growth of plants and 

 light is a generally recog- 

 nized fact. This relation 

 is particularly emphasized 

 in our glass houses during 

 the winter months. Dur- 

 ing that period cloudy 

 (lays are numerous, a suc- 

 cession of them* occurring not infre- 

 quently. The days also are short, so 

 that the total amount of light that 

 falls upon the plants during the winter 

 months is much less than that which 

 reaches them during the summer 

 months. 



The general effect of light on growth 

 is to retard it. Plants groWn in good 

 light, are, as a rule, shorter than sim- 

 ilar plants grown in weak light. It is 

 largely because of this relation be- 

 tween light and growth that we have 

 developed the practice of reducing the 

 temperature in our greenhouses at 

 night, for, as is well known, higher tem- 

 peratures stimulate the plant to a 

 greater growth rate, while lower tem- 

 peratures retard it. In other words, 

 by means of shifting the temperature 

 the grower aims to establish a proper 

 balance between the influence of light 

 on the one hand and the influence of 

 temperature on the other. If the ad- 

 justment is properly done, the result is 

 good growth in quantity and in quality 

 as well. 



Retarded Plant Growth. 



The influence of light is manifested 

 not only in the elongation of the stem, 

 which is the usual criterion of growth, 

 but the effects are evident in the en- 

 tiro form and structure of the plant. A 

 plant grown in weak light is deficient 

 in green color, the stem is thin and 

 weak, it has long internodes and the 

 leaves are poorly developed. A plant 

 grown in good light has a shorter but 

 stronger stem; the leaves are well de- 

 veloped and possess abundant green 

 color. 



Light also affects the production of 

 flowers. Every florist will testify that 

 a spell of cloudy weather is accom- 

 )ianied by a season of fewer blooms. 

 Flower production seems to be depend- 

 ent upon certain environmental condi- 

 tions which are more or less specific. 

 Tn other words, the conditions which 

 permit good vegetative growth — that 

 is, the production of stems and leaves 

 — are not the same as those which are 

 conducive to flower production. We 

 cannot draw a definite line of separa- 

 tion between flower production and 



By Dr. P. A. LEHENBAUER. 



NO INTBODVCTION NEEBtU. 

 Readers of The Review everywhere 

 have benefited by the helpful service to 

 Illinois florists of Dr. P. A. Lehinhauer, 

 head of experimental work in floricul- 

 ture at Vrbana, through the publication 

 in these columns of his papers before 

 Illinois trade bodies. His underslandiiu/ 

 of florists' problems and his practical 

 view of scientific experiments have won 

 for him widespread appreciation. He is 

 now writing for The Review a series of 

 articles of much interest and value to 

 growers, the first of which appears an 

 this page. 



vegetative growth, for these two phases 

 merge one into the other; nevertheless, 

 each seems to respond in its own way to 

 certain influences. In a later article I 

 shall discuss this more fullj', particular- 

 ly in relation to the use of fertilizers. 

 It is my purpose at present to point out 

 some of the facts which we have 

 learned about the effects of light on 

 vegetative growth and reproduction. 

 Kxtensive experiments carried on by 

 Garner and Allard, of the U. S. Depart- 

 ment of Agriculture, have established 

 facts which, it seems to me, are highly 

 significant in this respect. Tlnfor- 

 tunately, the plants which were used in 

 tliese experiments were not the kind 

 which are grown l)y florists; neverthe- 



less, it is probable that many of the 

 results are applicable to some of our 

 greenhouse plants and it is for this 

 reason that I feel justified in bringing 

 the facts to the attention of florists. 



Some fourteen years ago there was 

 found a strain of tobacco plant which 

 grows to an abnormal height and pro- 

 duces an abnormally large number of 

 leaves. The individual plants of this 

 strain grow to the extraordinary height 

 of from ten to fifteen feet, while the 

 plants of the old strain grow but a 

 few feet in height. It is quite appar- 

 ent that such a strain of tobacco, pro- 

 ducing a larger amount of leaf material, 

 is of great commercial importance. It 

 is also a significant fact that this strain 

 breeds true and always produces this 

 character known as gigantism. How- 

 ever, in the latitude about Washing- 

 ton, D. C, where the plant is grown, it 

 does not blossom in the field, ao seeds, 

 consequently, are produced and this is a 

 decided handicap in the culture of this 

 strain. If, however, plants which have 

 been growing outdoors all summer are 

 transplanted into the greenhouse late in 

 summer, blossoms will soon appear and 

 seed is formed in abundance. • The re- 

 sults are similar if the plants in the 

 field are cut back and only the stumps 

 planted under glass. If seeds are 

 planted in the greenhouse Jn the fall, 

 the resulting plants will grow to a 

 height of five feet or less and then 

 produce abundant flojvers. Similar seed 

 sown in the spring outdoors will pro- 

 duce plants which grow to ;i height of 

 from ten to fifteen feet, but which will 

 produce no flowers. 



Similar Seeds Differ. 



What is the explanation of these 

 phenomena? It is but natural to sup- 

 pose that the conditions for growth in 

 the greenhouse are different from con- 

 ditions outdoors and that this accounts 

 for the different behavior of the plants 

 in the greenhouse. In the jjreenhouse 

 the temperature is more uniform than 

 it is outdoors and on the average lower 

 than it is outdoors during tlie growing 

 season. The moisture of both soil and 

 air, the soil fertility, the carbon dioxide 

 content, as well as light conditions, are 

 more or less unnatural under glass. We 

 may also reason that it is the season of 

 the year which determines whether the 

 plant will produce flowers or whether 

 it will continue in the vegetative stage. 

 During the winter months the days are 

 short, while during the summer months 

 tlie days are long. In other words, the 

 qu;intity of solar light is less than it 

 is during the summer months, for not 



