GERMINATION 25 



in the open under shade. This is, however, more be- 

 cause of controlled moisture than of light. Paper and 

 muslin are popularly used for shading. (Figs. 15, 18.) 

 When the plantlets have two or more true leaves the 

 shade may be removed. 



40. Influence of sunlight on seed germination. Experiments in 

 Germany show that in nearly every instance seeds subjected to direct 

 rays of the sun were retarded in germination, although the effect on 

 the total germinative ability was not influenced in any appreciable 

 degree, the total number of germinations in each lot being practically 

 the same. One lot was germinated wholly in the dark, another re- 

 ceived sunlight 44 days, while the control lot was germinated out of 

 the direct rays of the sun. 



41. Seedlings grown without light. A. Bergerstein, a German in- 

 vestigator, grew seedlings of more than 100 species of gymnosperms 

 to determine the effects of light and darkness on them. His general 

 conclusions are that except Ginkgo and Ephedra the seedlings be- 

 come green even in the dark. The rapidity of coloration varies with 

 the temperature. Cycas and Zamia, even under favorable tempera- 

 tures, failed to develop chlorophyll in the total absence of light. 



- Among many conifers, chlorophyll is formed in the dark, both in the 

 cotyledons and the hypocotyl (except in LarLv). Araucaria pro- 

 duced it in branches developed while in the dark several weeks. In 

 Abies and Cedrus the embryo, even in dormant seeds, contains 

 chlorophyll. In other species the seedlings begin to turn green be- 

 fore the seed coat is broken or shortly after the emergence of the 

 radicle. Conifer seedlings in the dark have shorter roots and 

 cotyledons, but larger and thicker hypocotyls than similar plants 

 grown in the light. 



42. Oxygen is usually in ample supply for germination. 

 It is always present in soils neither tightly inclosed nor 

 water soaked. Water plants (lotus, water lily) have 

 special ability to germinate under water. 



43. Depth to plant. Deep planting is unfavorable to 

 germination, first, because the supply of oxygen is re- 

 stricted and, second, because the seedlings may be unable 

 to reach the surface, especially if the soil is hard. Under 

 glass the same species of seeds may be planted at twice 

 the depth employed in the open. After planting, the soil 

 should be firmed lightly (Fig. 20) to avoid washing when 

 watering. If the soil is hard and likely to bake, apply a 

 light mulch of old compost in the rows. 



