so HEREDITY AND EVOLUTION IN PLANTS 



40. 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 inheri- 

 tance 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. 



41. Inheritance and Reproduction. — Inheritance is, of 

 course, inseparably hnked with reproduction and may be 

 studied in connection with the three following types : 



1. In vegetative propagation, e.g., by means of tubers, 

 cuttings and "slips," bulbs and bulbils, gemmae, "run- 

 ners," scions, vegetative rejuvenation or "budding" (Fig. 

 35), etc., the new plant is obviously only a portion of the 

 vegetative tissue of the parent plant, iso lated and growing 

 independently by itseK. The separationof the propagating 

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

 ical and artificial. The protoplasm remains unaltered by 

 the act of separation, reduction divisions of cell-nuclei are 

 not involved, and the inheritance, except in bud-varia- 

 tions, is unaffected by the change. This is evident in those 

 cases where the isolated piece is grafted upon another 

 plant; the specific or varietal characteristics of the scion 

 are seldom, if ever, affected by the stock. Thus, in the 

 experiment illustrated in Fig. 36, a tomato stem was 

 grafted upon a tobacco plant, and upon the tomato were 

 grafted three other species — Solanum nigrum, Solanum 

 integrifolium, and Physalis Alkekengi. Each species was 

 apparently not in the least altered by this drastic change 

 in the conditions of its life. 



2. In asexual reproduction by spores the situation is 

 quite similar to that in vegetative propagation, but in 



