HEREDITY OF ACQUIRED CHARACTERS 197 



manent in the life of the plants, so that the fleshy stem, to- 

 gether with its other characteristics, are reproduced whenever 

 the plants in question are raised from seed as in England, that 

 is under totally different conditions of life from those of their 

 natural habitats. 



So that not only the tendency but the power to produce 

 the actual modifications is hereditary. 



The above cases illustrate what happens to plants where 

 they grow in very dry, hot and barren regions. Let us now 

 see what takes place in water. 



A common feature in aquatic dicotyledonous plants is to 

 have the blades of their submerged leaves finely divided into 

 capillary segments. This occurs in numerous plants of as many 

 famiUes and of no affinity between them. The following are a 

 few examples : the water-crowfoot [Ra?iu?tculacece) ; Caboinba, 

 {JVymphceacece) ; water milfoil, {HaloragecE) ; Helosciadium in- 

 undatum {^UmbellifercB) ; water violet {Primuiaceae) ; Cerato- 

 phyllum {Ceratophyllece) ; and many others might be named. 



Moreover, not only do we see completely formed leaves or 

 leaflets in allied terrestrial species as of buttercups compared 

 with Ranunculus trichophyllus, or in Helosciadium nodiflorum, 

 etc., but both forms of leaf may be borne by the same plant, if 

 it have some floating on or raised above the water, and others 

 below it ; as in Raiiunculus heterophyllus, Cabomba, Proser- 

 pinaca, etc. . 



Indeed, it frequently happens that a leaf is so situated that 

 half of it develops under water and the other half in the air. 

 When this is the case, the former is divided into fine, thread- 

 like segments, and the latter half is flat and complete. More- 

 over, the anatomical tissues of the former are adapted to a sub- 

 merged life, while these of the latter are equally so for the air. 



It not infrequently happens when Ranunculus trichophyllus, 

 which is normally entirely submerged, is growing very crowded 

 in a small pond, that some of its branches are forced upwards 

 so as to grow into the air; then all parts above the water-line 

 grow in adaptation to an aerial existence ; all below the line 



