XXIII 



EFFECT OF THE VISIBLE SPECTRUM UPON THE 

 GERMINATION OF SEEDS AND FRUITS 



William Crocker 



Historical. Conditions modifying the effect of light upon germination: Seeds that are 

 favored by light — Loranthaceae and other epiphytic forms, Gesneriaceae, Chloris ciliata, 

 Poa, Ranuncidus sceleratus, Onagraceae, Lythrum, other seeds. Seeds inhibited by light — 

 Phacelia tanacetifolia, Nigella, Liliaceae, other seeds. Effect of various regions of the 

 spectrum. Dosage of light required. Theories of light action. Summary. References. 



HISTORICAL 



Early investigators, Ingenhousz 1788, Humboldt 1794, Senebier 1797, 

 Saussure 1804, Heiden 1859 (66, page 432; 79), concluded that light had 

 no effect or a detrimental effect on seed germination. Unfortunately, 

 Ingenhousz, Senebier, and others (79, page 240) worked with light- 

 indifferent seeds such as mustard, beans, and peas. Caspary (11) was 

 the first to claim that light was favorable for the germination of any sort 

 of seed when he found that Bulliarda aquatica germinated well in full 

 sunlight but poorly in diffuse light. This work must have been over- 

 looked, for in his "Handbuch der Samenkunde" Nobbe stated that 

 all previous investigators had found sunlight not only unnecessary but 

 even injurious for initiating germination. He suggested that the detri- 

 mental effect of light might be due to excessive heating and evaporation. 



Peyritsch and Wiesner (103, pages 182 and 183) found light necessary 

 for the germination of Viscum album seeds. Kraus reports that in 1878 

 Wagner (55, page 410) had shown that light favored the germination 

 of Poa achenes, but it was Stebler's work in 1881 (92) on the favorable 

 action of light on the germination of various grass achenes that gave the 

 great stimulus to investigation in this field and aroused the antagonism 

 of Nobbe, Stebler found that under controlled temperature conditions 

 Poa nemoralis gave 1 to 3 per cent germination in darkness and 53 to 

 62 per cent in daylight, while P. pratensis gave to 7 per cent in darkness 

 and 59 to 61 per cent in light. Light from a gas lamp proved as effective 

 as sunlight. Light favored the germination of various other genera of 

 grasses: Festuca, Cynosurus, Alopecurus, Holcus, Dactylis, Agrostis, Aira, 

 Panicum, and Anthoxanthum. Quick-germinating seeds such as beans, 

 peas, and clovers were indifferent to hght. Stebler mentioned that 

 Leitgeb and Borodin had found light necessary for the germination of 

 spores of some liverworts and ferns, and Pfeffer for the germination of 

 the gemmae of Marchantia polymorpha. 



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