296 The Phenomena of Morphogenesis 



from the plant, are the ones used by P. R. White in his first tissue cul- 

 tures (1939). He found later that they retained their specific proper- 

 ties in culture for years and continued to grow as tumors when grafted 

 into young stems of Nicotiano glauca (1944). Satina, Rappaport, and 

 Blakeslee (1950) studied the development of somewhat similar tumors 

 appearing in fertilized ovules from incompatible crosses in Datura. 



Changes in cellular character are sometimes associated with abnormal 

 growth. Prothallia of some ferns, when grown in culture, often produce 

 various types of proliferations (Partanen, Sussex, and Steeves, 1955). 

 Some of these remain essentially prothallial in character and show no 

 fundamental deviation from normal. Their cells are still able to re- 

 generate normal prothallia again. Certain tumor-like forms, however, are 

 modified much further, for they have lost this ability. This loss is ac- 

 companied by a modification in cellular character, visible as an increase 

 in chromosome number from In to 3n or 4n. Such forms may be com- 

 parable in a sense to crown gall. White and Millington (1954) have 

 described a woody, nonbacterial tumor in spruce which begins in a 

 single cambium cell. This has been altered, physiologically or geneti- 

 cally, and forms a mass of abnormal tissue. The plant becomes what is 

 essentially a sectorial chimera. 



Various aspects of the problem of plant tumors have been discussed 

 by P. R. White (1951), de Ropp ( 1951a ), Klein and Link (1955), and 

 others. 



Tissue Cultures. Tissue cultures can hardly be called tumors or galls, 

 but in them the normal organization of the plant has disappeared to a 

 greater extent than in any other case here discussed. A book on mor- 

 phogenesis is not the place to consider this subject in any detail but it 

 does have some important morphogenetic implications that should be 

 mentioned. So-called tissue cultures of plant material on sterile media 

 have been studied actively in recent years, and for an account of them 

 the reader is referred to the publications of the pioneers in this field, 

 especially P. R. White, Robbins, Gautheret, and Nobecourt. 



Animal tissues have been cultured for half a century but it was much 

 more recently that this was done successfully with plants. The problems 

 involved were first clearly stated by Haberlandt, who himself failed to 

 grow isolated cells from higher plants in artificial media. A necessary 

 prerequisite for the success later attained was the development of 

 satisfactory media consisting of pure substances of known chemical 

 character, including salts, carbohydrates, organic nitrogenous materials, 

 vitamins, and growth substances. The media developed by the early 

 plant workers were superior to the sera and other complex and little 

 understood ones previously used by tissue culturists. 



The first plant cultures were not tissue cultures in the strict sense that 



