GERMINATION OF POLLEN 347 



nivalis from i to 7 per cent., Allium ursimim from 3 to 5 per 

 cent. Only the pollen of the primrose germinated in water 

 as well as in sugar solution. Lidfors (1896), however, 

 obtained germination in water with plants belonging to 

 61 famihes, for example, with Lysimachia, Lobeha, Urtica, 

 Parietaria. Germination occurred only in distilled water, 

 not in water containing salts. 



There are, however, many cases known in which germina- 

 tion does not occur under such simple conditions, and where 

 the presence of substances excreted by the stigma seems to 

 be essential. Burck (1900) found that the pollen of Mus- 

 saenda germinated only when a piece of the stigma was 

 placed in the water ; the influence of the stigma could be 

 replaced only by laevulose which was effective in traces. 

 Here the regulation of water supply could not explain the 

 effect, nor could the necessity of food substances. The case 

 is as yet unanalysed. The chief interest lies in the possibility 

 of some regulation of the germination of the pollen grain. 

 Molisch was unable to obtain germination under any 

 artificial conditions with the pollen of certain Compositas, 

 e.g. Taraxacum officinale, Chrysanthemum Leucanthemum, 

 Urticaceae, e.g. Urtica dioica, Cannabis sativa, Malvaceae, 

 e.g. Althcea officinalis, Malva syhestris. Pollen of the 

 Ericaceae, e.g. Rhododendron, Azalea, germinated only in 

 acid solutions, especially in malic acid. The pollen of 

 Pavetta javanica can germinate only on the stigmas of that 

 species or of the closely related P. fulgens, but not on those 

 of other species of the genus. 



It is evident that in many species pollen can germinate 

 under a great variety of conditions, and it is probable 

 that such pollen frequently germinates on strange stigmas. 

 Whether fertilisation follows depends on other factors, in the 

 first place of course on the closeness of the species to each 

 other. In other cases pollen can germinate only in special 

 conditions, which, in nature, are provided by the stigmas of 

 the particular species in question. Even where only a definite 

 range of concentration of sugar is required the chance that 

 germination may occur before the pollen reaches the stigma 



