Nov., 1923] 
BAILEY-CAMBIUM AND DERIVATIVE TISSUES 
5 07 
Stratified Gambia 
Dicotyledons 
D. Vascular tissues highly specialized 
Species 
Max. 
Ave. 
Min. 
Grewia multiflora Juss...... 
370 
250 
160 
Thespesia populnea (L.) Soland. ex Corr... 
280 
250 
210 
Bombycidendron Vidalianum Merr. et Rolfe.......... 
430 
360 
320 
Heritiera littoralis Dryand...... 
360 
300 
270 
Kleinhovia hospita L...... . 
480 
360 
270 
Pterospermum niveum Vid.... 
430 
370 
320 
Tarrietia sylvatica Merr....... 
340 
280 
210 
Sterculia foetida L.... 
450 
370 
320 
Robinia Pseudo-Acacia L.. 
210 
170 
140 
Dio spy ros virginiana L..... 
520 
410 
320 
Average. >...... 
390 
310 
250 
Basis: 50 measurements of fusiform initials. 
Probable errors of individual averages 10-15 percent. 
cipient stages of stratification. Furthermore, the variability in the size of 
adjacent fusiform initials in stratified meristems (table 1) is due, at least in 
part, to the fact that many of the anticlinal divisions are somewhat oblique. 2 
How much significance should be attached to the close parallelism in the 
sequences of changes in the cambium and vascular tissues? Is the pro¬ 
gressive reduction in cell size in the lateral meristem due to the increasing 
specialization of the vascular tissues, or vice versa? Many morphologists 
interpret such correlations as due to cause and effect. There is, however, 
a very considerable element of uncertainty in so doing, where the basis of 
comparison is time, as Karl Pearson has so clearly shown. Thus, in the 
absence of reliable collateral evidence it is not possible to determine whether 
the changes in the cambium .are due to those which occur in the vascular 
tissues or vice versa, or whether the parallel sequences are both due to some 
third factor or group of factors. 
Summary and Conclusions 
1. There are two fundamental types of cambial activity in the vascular 
plants: one characteristic of the Calamariales, Sphenophyllales, Lepi- 
dophytineae, Cycadofilices, Gymnospermae, and less differentiated (struc¬ 
turally) Dicotyledoneae, and the other of certain highly specialized di¬ 
cotyledons. 
2 . In the former type the fusiform initials are not arranged in regular 
rows. The anticlinal divisions are pseudo-transverse and the products of 
2 The size and the arrangement of the fusiform initials is also modified by the ray 
initials, new aggregations of which are periodically carved out of the elongated elements. 
