244 SEEDLINGS OF AQUATICS [CH. 



comparative cultures of the achenes of Alisma Plantago, ex- 

 amined at the end of ten days, those in which the protective 

 coats were intact, had not germinated at all, while 98 per cent, 

 of those whose walls had been ruptured, had begun to sprout. 

 The reason why preliminary drying favours germination, may 

 possibly be that it gives rise to some cracking of the seed coats ; 

 a speeding-up of germination also occurs, in some cases, if the 

 seed passes through the alimentary canal of a bird 1 , a result 

 which again may be due to some disintegrating chemical or 

 mechanical action exerted on the wall. Freezing may also assist 

 germination by means of its effect on the outer covering of the 

 seed 2 . 



It should be noted, that delayed germination, though 

 specially characteristic of water plants, is by no means peculiar 

 to them. That the causes which bring it about are of a similar 

 nature in aquatics and terrestrial plants, is indicated by the fact, 

 well known to gardeners, that a large proportion of such seeds 

 as those of Canna, fail to germinate unless the shell is filed 

 through. The phenomena of delayed germination suggest that 

 Nature, in her solicitude for the protection of the embryo, is 

 liable to defeat her own ends by enclosing it in a prison from 

 which it can only escape with difficulty. 



The germination and development of the seedling in aquatics 

 vary according to the natural affinities of the plants in question, 

 and are characterised by few peculiarities related to the environ- 

 ment, except a very frequent reduction of the primary root. 

 In Utricularia (Fig. 67, p. 100), Stratiotes abides*, Hydrocharis y 

 Ruppia, Ceratophyllum (Fig. 55, p. 86), the Podostemaceae, 

 Nymphaea lutea, Aldrovandia^, Hippuris, Naias, Trapa 5 , etc., 

 the radicle is either quite undeveloped or very short-lived. In 

 Aponogeton distachyus 6 the primary root does not attain to more 

 than 0*5 cms. in length, and eventually it disarticulates by 



1 Guppy, H. B. (1897). 2 Guppy, H. B. (1893). 



3 Irmisch, T. (1865). Korzchinsky, S. (1886). 



5 Queva, C. (1910); see also Fig. 160, p. 247. 



6 Sergueeff, M. (1907). 



