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 



FIG. 270. Ranunculus aqua- the land plants haVC broad, Seg- F p- W- Potamegeton 

 tilts A Seedling ger lucens. seedling 



minating' in water. B. mented blades, while the Water Sima^tbearine 



H'-WSSM form has only a few thread-like 

 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, 



SeeaHng wTthTm- adventitious TOOtS nCVCr appear On Fl - *- Ceralophyllum 

 porary primary root aemer sum. beedling 



bearing cluster of this Dlant T th C ? t / led . n i rat ^~ 



root-hairs. (After Ullt5 P ld - llu cle and first leaf pair. 



irmisch.) In N u phar 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 germinate in the muddy 

 substratum, but as the embryo emerges the newly formed tissues 



