THE LARGER AQUATIC VEGETATION 



193 



the embryo in the seed, but in germination this rudiment is sup 

 pressed in its development and never gets to be a real root. 



The seeds of Ranunculus aquatilis will germinate 

 either on land or in water but the development of the 

 seedling is not alike in each case 

 (Fig. 270). The seed leaves are 

 similar, except that those of the 

 land seedling are a little wider in 

 proportion. The true leaves of 

 the land plants have broad, seg- 

 mented blades, while the water 



Fig. 270. Ranunculus aqua- 

 tilis. A. Seedling ger- 

 minating in water. B. 

 Seedling germinating on 



land. (After Askenasy.) foHii has ouly a icw thread-like 



Fig. 271. Potamogeton 

 lucens. Seedling 

 with temporary 

 primary root bearing 

 cluster of root-hairs. 

 (After Warming.) 



branches with little indication of a distinct blade. 



Potamogeton lucens and Naias major send out a primary root 

 from the seed upon which a cluster of root-hairs soon develops to 

 help anchor the plant. But this primary root is not lasting and is 

 soon succeeded by adventitious roots which spring 

 from the joints of the runners which developed in the 

 meantime (Figs. 271 and 272). 



Ceratophyllum furnishes a very interesting instance 

 of suppressed root development. There is present 

 in the embryo of the seed a rudimentary root, but 

 it never develops into an organ of attachment or 

 serves for the entrance of mineral salts. When the 

 seed germinates this rudiment of a root pushes out 

 far enough to let the plumule rise 

 from between the emerging cotyle- 

 dons and then its growth practically 

 stops (Fig. 273). So far as known, 

 adventitious roots never appear on ^'j,^lfsum.'''''SZ 



J.T-* „1 i. with cotyledon, radi- 



tniS plant. cle and tirst leaf pair. 



In Nuphar and Brasenia the seed- ^* ^" 

 ling escapes from the seed by pushing out a plug which before 

 germination occupies the passage intended for the exit of the 

 young plant. 



The seeds of Utricularia commence to genninate in the muddy 

 substratum, but as the embryo emerges the newly formed tissues 



Fig. 272. Naias major. 

 Seedling with tem- 

 porary primary root 

 bearing cluster of 

 root-hairs. (After 

 Irmisch.) 



