The Living Materials 49 



work with. The only intercalary meristem which 

 has been successfully grown is that from the pro- 

 cambial region of tobacco (White, 1939, 78). If 

 the procambial tissues of fairly succulent plants 

 such as tobacco or squash are carefully excised 

 under aseptic conditions (see later) and placed on 

 a nutrient substratum, proliferation will occur, 

 the newly formed callus tissue can be removed 

 from adherent non-proliferating medullary ele- 

 ments, and a rapidly growing "pure-line" callus 

 culture will result which can be propagated in 

 series indefinitely. This is one of the most im- 

 portant types of culture obtained to date and will 

 be discussed in more detail later (Fig. 18). 



If, moreover, the cambium is taken from peren- 

 nial plants having secondary thickening, and for 

 this purpose trees of fairly good size offer fewer 

 mechanical difficulties than do smaller plants, and 

 is placed on a nutrient, a similar proliferation 

 occurs, the product of which can be treated in the 

 same manner (Gautheret, 1934, 67, 1935, 15, 1937, 

 68, 1938, 69, 70, 1939, 71, 72, 1940, 73). When es- 

 tablished in culture, it behaves much as do cul- 

 tures derived from procambium. Gautheret has 

 been especially successful with this type of cul- 

 ture and has made a number of very interesting 

 experiments therewith (Figs. 38, 64). The cul- 

 tures of callus from carrot root, carried out by 



