170 



HARDWICKE'S SCIENCE-GOSSIP. 



the oak. This development obtained rest by the oak- 

 forest becoming the dominant forest of the land. The 

 oak's domination became disturbed by the intrusion 

 of man into the forest, and perhaps at the same 

 time by that of the beech, which is master of the oak. 

 In many localities the new species made great 

 progress ; but natural and social conditions impeded 

 for many centuries its extension ; when these were 

 removed the beech renewed the contest in all places. 

 The new beech-forest now occupied all forest districts, 

 as a result to which the agency of different other 

 species had led. The fir, the aspen, the birch, and 

 the oak, had all contributed to the formation of a soil 

 suitable for the beech-forest, which in its natural, 

 and not maltreated state, has first gained general 

 extension in our days. In its completeness it presents 

 itself with high, straight trunks, whose heads form an 

 enclosing leafy roof. Seen from below, the heads 

 appear small, but in reality are so large as to include 

 a third or fourth part of the tree's height, and the 

 leafy roof is so close, that light enough cannot 

 struggle through to support the life of any species of 

 tree upon the ground. Grass cannot grow in a good 

 beech-wood ; of the numerous herbs, but very few 

 kinds can be content with the sparse supply of light 

 which reaches the soil when their leaves unfold. It 

 is especially the wood-ruff and the wood-sorrel which 

 form green garlands among the brown beech-leaves, 

 and are living witnesses that the mutual bearing and 

 order of the trees are what they ought to be. 



The following chapters are an attempt to show in 

 what manner the natural conditions either do not 

 hinder, or highly favour the aggressive tendency of 

 the beech in the Danish forest, and to investigate the 

 influence which heat, soil, moisture, light, and power 

 of self-sowing exercise upon the distribution of tree- 

 species in the forest. 



DAISY SLEEP. 



WHEN cycling along the highways and by- 

 ways of South Beds, during some of the 

 sunny afternoons of the spring of 1S82, my atten- 

 tion was arrested by the contrast in appearance of the 

 hedgebanks on the opposite sides of the roads. Those 

 with a northerly or easterly aspect, wore a dull 

 yellowish-green hue, by reason of the abundance of 

 mosses on them, whilst those with a southerly or 

 westerly aspect were gay with daisy blossoms. The 

 bright sunlight which encouraged the growth of the 

 latter, was fatal to that of the former, which 

 luxuriate in the comparative shade and moisture of 

 the cooler side. Or, in other words, when these 

 banks were constructed, only those plants, to which 

 direct sunlight was advantageous maintained their 

 hold in the struggle for existence, whilst the others 

 either perished or were but feebly represented. 



These contrasts just referred to, were, however, not 



always so strongly marked. On cloudy days, or as 

 twilight came on, there was less dissimilarity between 

 the two. The sides that had been all aglow with 

 the white-rayed daisy heads were almost as sombre 

 as the moss-covered banks. And why ? The daisies 

 had gone to sleep ; or, in scientific parlance, had 

 assumed their nocturnal position. The white ray- 

 florets had folded inwards, covering the golden discs, 

 and had themselves been partially concealed by the 

 green linear bracts which surround the flower-heads. 

 By these complicated movements, to which the term 

 nyctitropism has been applied, the pollen is protected 

 from the night dews and rain, and is reserved for 

 those insects whose visits are necessary to ensure 

 pollination. This is the transference of the pollen to 

 the stigmas, without which fertilisation of the ovules 

 would not take place, and hence no seeds would be 

 formed. Since these insects fly about only during 

 the hours of bright sunshine and frequent the sunniest 

 spots, it is evident, that only in such situations and 

 during such periods, expanded flower-heads are of 

 greatest service to the plants. It has also been men- 

 tioned to the writer by a keen observer, that when 

 fertilisation has been accomplished, the flowers are 

 less sensitive to the variation of light and shade. 

 This has been confirmed by recent original observa- 

 tions. 



Thus far the subject presents but little difficulty ; 

 when, however, we come to enquire by what forces 

 these mechanical movements are effected, much 

 caution should be exercised in attempting to reply. 

 When thinking over the subject, with the hedge- 

 banks rapidly passing in review, as one sped pleasantly 

 onwards, the problem forced itself on one's mind, and 

 the following is an attempt at its solution. 



It may be presumed that at least two forces are 

 concerned, viz., the varying turgescence of the interior 

 and exterior sides of the involucral bracts ; and, the 

 stimulus of direct sunlight on the ray florets. The 

 latter is probably the most potent factor, and it is 

 also accompanied by varying turgescence of the cells 

 in the organs affected. 



Upon the examination of any bud of a daisy, it will 

 easily be understood that during its development the 

 exterior or lower sides grow more rapidly than the 

 interior or upper. The difference though slight, is 

 real, and is demonstrated by the fact that the convex 

 side must necessarily be longer than the concave ; 

 and as they both start from the same growing-point, 

 the growth of the former must have been greater than 

 that of the latter. When they have attained to com- 

 parative maturity, growth in length is reduced to a 

 minimum, although perhaps not absolutely arrested. 

 During the hours of the night previous to the first 

 opening, the air surrounding the flower is compara- 

 tively moist and cool, and transpiration is hence but 

 slight. As soon as the sun's rays fall upon the spot, 

 the temperature is rapidly raised, and transpiration 

 from the exposed surfaces of the involucral bracts is 



