390] CELL AND NUCLEAR DIVISION IN FULIGO VARIANS 241 
Hofmeister believed that cell division takes place according 
toasimple mechanical law. The new cell wall always cuts the 
axis of most intense. growth at right angles (8, p. 127). It is 
plain that such a principle as this can have no application in 
interpreting the division of the masses of protoplasm in sporanges 
whose growth is complete, the accompanying tensions, as may 
be fairly assumed, having also reached a condition of equi- 
librium, 
Sachs (20 and 18, p. 22) follows Hofmeister in regarding the 
growth and division of the single cells as subordinate to the 
growth of the vegetative point as a whole. From a study of 
the arrangement of the cells in the growing point of the higher 
‘ryptogams and flowering plants, he has developed the law of 
the rectangular intersection of cleavage planes in the successive 
cell divisions. He regards this as the most universal law of 
Sttucture in the plant world, and holds that it is independent of 
all phylogenetic relations, and not a result of natural selection. 
As is well known, he holds that the outer form of the growing 
organ is the primary determining factor for the orientation of 
the Cleavage planes. The periclines conform directly to the 
surface of the embryonic organ. The anticlines cut the peri- 
one at right angles, and if division is to occur in three dimen- 
ns the transversals also appear in a third plane at right angles 
ot. Sachs believes that the relations thus expressed 
es undamental a nature as to be comparable to those 
Hs ing the relations of the axes of a crystal. The cellular 
Reccca, ystal to the arrangement of its faces and their 
S angles. The form of a growing point is determined 
and selection when given the direction of the 
2 th Planes, is at once known. Such fundamental relations 
ese, 
m 
Sach, La hanomorphoses. The principle thus developed by 
Rent of sh generally accepted as explaining the arrange- 
€ cell walls in the growing points of the higher plants, 
