544 STRUCTURE AND LIFE HISTORIES 



herited may be expressed; this is illustrated when chil- 

 dren resemble, not their parents, but their grandparents. 

 Here the parents transmitted an inheritance which, in 

 them, found no expression. A remarkable illustration of 

 inheritance without expression is seen in the case of the 

 alternation of generations (pages 181-183). The initial 

 protoplasm of the sporophyte is all inherited through the 

 fertilized egg from the gametophytes, but most of the 

 gametophytic characters do not appear in the sporophyte, 

 nor do the typically sporophytic characters find expres- 

 sion in the gametophyte.^ 



465. Inheritance Versus Heredity. — As stated above, 

 the inheritance is that which is actually transmitted from 

 parent to offspring. The fern-spore, for example, is the 

 inheritance of the fern gametophyte from the sporophyte. 

 Heredity is the genetic relationship that exists between suc- 

 cessive generations of organisms. The relation between two 

 brothers and their parents is similar — it is one of heredity; 

 their inheritance may be quite different. 



466. Inheritance and Reproduction. — Inheritance is, of 

 course, inseparably linked with reproduction and may be 

 studied in connection with the three following types : 



I. In vegetative propagation^ the new plant, as noted in 

 Chapter XVII, is obviously only a portion of the vegeta- 

 tive tissue of the parent plant, isolated and growing inde- 

 pendently by itself. The separation of the propagating 

 piece from the parent is often (though not always) mechan- 



' The chlorophyll, of course, is an exception. But the osmotic strength 

 of the cell-sap is a different expression in gametophyte and sporophyte, 

 otherwise the young sporophyte could not live parasitically upon the 

 gametophyte. 



' E.g., by means of tubers, cuttings and "slips," bulbs and bulbils, 

 gemmffi, runners," scions, etc. 



