INFLUENCE OF LIGHT. 507 



very little altered, and in the central portion the onlj- change is that the lobes and 

 teeth become shorter and less clearly marked. 



In order to ascertain the effect of covering plants with earth, numerous bulbs 

 of a species of Tulip (Tulipa Gesneriana) were planted at the same depth in one 

 garden bed, and in another some corms of the Spring Crocus (Crocus vernua). 

 Earth was heaped over these bulbs and corms in successive heights of 5, 10, 15, 20, 

 25, 30, 35, 40, 45, and 50 cm. Naturally the leaf -tips and flower-buds were first 

 seen in the places where the bulbs were only covered with 5 cm. of soil; in both 

 beds the development was delayed — in the other cases in proportion to tlie height 

 of the soil above the bulbs. Some flower-buds of the Crocus appeared above the 

 20 cm. of soil, one of the Tulip above the 30 cm. Numerous leaf-tips of the 

 Crocus appeared above the 35 cm., and a few of the Tulip above the 40 cm. of soil. 

 The perianth-tube, the peduncle and the foliage-leaves were almost twice as long as 

 those which had developed under only 5 cm. of soil. The flowers were smaller, and 

 unfolded just above the soil; the leaves were narrower and pale yellow in colour 

 as far up as they were covered with the soil. Neither the Crocus nor the Tulip 

 raised their leaves higher than 40 cm. Apparently the reserve-materials stored in 

 the corm and bulb-scales were not sufficient for a further elongation. The stems 

 and leaves of the Crocus and Tulip thus exhibit alterations similar to those 

 observed in the sprouts of Potato-tubers in a dark cellar. 



We should expect that if moisture and lack of light produce elongation of 

 shoots and various alterations in leaves, a brilliant illumination would have the 

 opposite efiect on growing plants. This is indeed the fact. Plants which have been 

 for a year in the shade and have been placed at the beginning of their development 

 in the following year in the sun display shorter internodes and firmer leaves; they 

 blossom more abundantly, the flowers are of a deeper hue, and in many cases a 

 covering of hairs is formed over the green portions. It is not necessary to mention 

 how far transpiration, which is much more active in the sun than in the shade, is 

 concerned in this; these alterations are certainly produced in the end by sunlight. 



The efifect of brilliant illumination is best seen by comparing plants grown from 

 similar seeds at dififerent elevations, but under identical conditions in other respects. 

 The results obtained in my experimental garden near the summit of tlie Blaser in 

 the Tyrol, at a height of 2195 m., during the years 1875-1880 illustrate this very 

 fully, and I will briefly recount them here. The seeds of some annual plants were 

 sown in September. The beds were covered with a layer of snow a metre thick 

 throughout the winter. The germination of the seeds took place in the following 

 year soon after the snow melted between the 10th and 25th June. The seedlings 

 therefore developed during the time when the sun was highest and the days longest, 

 and the young plants were exposed to a temperature not lower but rather higher 

 than that enjoyed by plants from similar seeds which began to develop in the 

 experimental beds of the Vienna Botanic Garden in March, when the daylight 

 lasted about 12 hours. The seedlings of several species (e.g. Gilea tricolor, Hyos- 

 cyamus albus, Plantago Psyllium, Silene Gallica, Trifolium incaniatum) were 



