Meristems 65 



but they doubtless differ physiologically. The subapical mother-cell zone 

 is perhaps comparable to a somewhat similar region in the root (p. 78) 

 where the rate of protein synthesis is lower than in surrounding cells. 



An attempt to follow cellular changes at the surface of living shoot 

 apices has been made by Newman ( 1956), using Tropaeolum and Coleus. 

 By an ingenious technique he was able to follow and draw, for as long 

 as 9 days, the divisions of individual surface cells. At the very tip of the 

 meristem he observed that divisions were frequent and believes that in 

 this region there is a small group of cells that may be regarded as apical 

 cells. His results fail to confirm those of Lance (1952), who reported 

 that divisions were infrequent at the very apex, as Plantefol's theory 

 (p. 156) assumes. 



There is a considerable literature dealing with the structure of the shoot 

 meristem in particular plants and under different conditions. Much of 

 this has morphogenetic interest. Cutter (1955), for example, finds that 

 the organization of shoot apices in eight saprophytic and parasitic species 

 of angiosperms is essentially like that in plants with normal nutrition. 

 Boke in a series of papers (1955 and earlier) described the stem apices 

 and shoot histogenesis in a series of xerophytes, especially Cactaceae. 

 Stant ( 1954 ) compared the shape of the shoot meristem in five species 

 of monocotyledons and found a relationship between this character and 

 the growth habit of the plant. In general, where the meristem is long 

 and narrow, as in Elodea, the plant has well-developed internodes. Where 

 it is relatively short and wide, as in Narcissus, the stem is much reduced 

 and the internodes very short. The size of the apical dome is essentially 

 the same in cucurbits with large fruits as in those with small fruits, and 

 differences in organ size do not appear until a short distance below the 

 tip of the meristem (von Maltzahn, 1957). The difference between the sin- 

 gle-gene maize mutant "corn grass" and normal corn arises in the 

 meristem, the mutant having a relatively larger meristem and a more 

 rapid production of leaf primordia (Whaley and Leech, 1950). Bouffa 

 and Gunckel (1951) examined 54 species of Bosaceae but found no sig- 

 nificant relation between the number of tunica layers and the taxonomic 

 position of the plant. The development of the shoot meristem from its 

 early appearance in the embryo has been studied by various workers 

 (Beeve, 1948; Spurr, 1949; and others). 



The implications of results from the study of the shoot apex for 

 morphological problems, especially the nature of the leaf, have been 

 considered by various observers. Philipson (1949) believes that the evi- 

 dence from this source supports the idea that the leaf is an enation and 

 not a consolidated branch system. 



Leaf primordia are formed in regular sequence below the dome of the 

 shoot apex, and it is here that many of the structural characters of the 



