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162 BOTANICAL GAZETTE [MARCH 
has, beside the dermatogen, sixteen cells which are to become 
differentiated into periblem and plerome. Some writers say that 
the periblem and plerome are differentiated very early, and they 
have even pointed out the first cell which is to produce pler- 
ome and the first which is to produce periblem, as if each 
cell were predestined to play a certain réle. Hanstein’s (3) 
classic account of Capsella, followed by the standard text- 
books, illustrates this idea; Fleischer (7) is equally definite 
in his description of Ornithogalum and Viola; and there is no 
doubt that their figures are accurate. Everyone who has cut 
Capsella knows how easy it is to duplicate most of Hanstein’s 
figures. It is possible, perhaps probable, that the theory is cor- 
rect in the case of Capsella, as it has a very regular embryo. 
In the other types which Hanstein considers, such an explana- 
tion is not so satisfactory. Fortunately, he does not attempt to 
apply the theory to all plants. Fleischer would apply it to 
dicotyls in general, but in his Asclepias one cannot distinguish 
periblem from plerome in early stages. It is evident that mono- 
cotyls, in many of which the plerome can hardly be called an 
independent system, must have a different explanation. 
In the more regular embryos of Salix a person with some 
ingenuity might imagine this early differentiation into periblem 
and plerome, but the usual forms would demand some other 
theory. In Salix there are no four cells, which with their pos- 
terity are predestined to form the plerome of the plant, as.in 
Hanstein’s Capsella, but, as will be shown, the differentiation of 
these tissues occurs very late in the development of the embryo. 
The relation between the suspensor and embryo in early 
stages is shown in figs. 68, 70, 77. It will be seen that the upper 
cell of the suspensor has divided by a longitudinal wall. A 
second longitudinal division, which may take place in embryos 
even younger than these, divides the upper cell of the suspensor 
into a plate of four cells (fig. 57). The dermatogen of the 
whole embryo, except the part contributed by the suspensor, is 
differentiated in embryos still younger than that shown in fig. 65- 
The dermatogen is the first of the primary tissues of the root tip 
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