302 



DICOTYLEDONOUS GERMINATION. 



plumule (figs. 528, 529 g) proceeds from between the two cotyledons, 

 and does not pierce through a sheath as in monocotyledons. The 

 root (fig. 528 r) is a direct prolongation of the axis, f, in a downward 



direction, separating from it at the collar, m, and the embryo is here 

 exorhizal (||, outwards). See ^[ 126. 



In Acotyledons, the spore (fig. 530) has no separate embryo in its 

 interior, but germinates from any part of the surface; hence it is called 

 heterorhizal (irepos, diverse). See ^[ 128. The spore may be considered 

 as a cellular embryo rather than a seed. 



630. Some seeds commence the process of germination before being 

 detached from the plant. This occurs in a remarkable degree in the 

 Mangrove trees, or Ehizophoras, which grow at the muddy mouths of 

 rivers in warm climates. Coco-nuts often begin to germinate during 

 a voyage from the tropics to Britain, and germinating seeds have 



Fig. 528. Germination of the dicotyledonous embryo of Acer Negundo. m, Collum, collar or 

 neck, r, Root (, Caulicule or stem, c c, Cotyledons, g. Gemmule or plumule. 



Fig. 529. Upper parfrof the same embryo more developed, c c, Cotyledons, g, Gemmule, 

 the first leaves of which are already expanded, t, Caulicule or stem. 



Fig. 530 Acotyledonous embryos or spores of Marchantia polymorpha, germinating. 1. Spore 

 in the early stage of germination. 2. In a more advanced stage. The spores are simple cells, 

 which elongate during germination at some point of their surface. They are heterorhizal. 

 They may be compared to naked embryos rather than to seeds. 



