GROWING POINT 45 
of the dermatogen, or in some cases, of the dermatogen 
itself, or, in still other cases, by the division of some of 
the cells of a common mass of initial cells from which the 
root cap as well as epidermis, periblem and plerome 
arise. On the growing points of stems, the new branches 
arise by the formation of secondary growing points at 
the side of the main -one, these having the same 
general plan. Those that produce the leaves often grow 
faster than the mai growing point and sur- 
round and protect it, thus forming a bud. 
60. As the growing point progresses, the 
cells formed in it come to lie further and 
further from the apex. They increase in size 
d pr pl, prd; 
and, after a while, cease to divide. Certain Ww 
of the cells remain meristematic a long while; pi'Sdecn, 
others become elongated, i.e. cease early to di- Paiblem. — 
vide transversely, and eventually become ret. %Fiew 
transformed into fibrous, tracheary, sieve tis- 
sue or collenchyma. Some cells merely enlarge and 
become parenchyma. ‘Thus, near the tip the cells will 
be found to be all meristematic, but further back, various 
kinds of tissues may be found. 
Laboratory Studies. (a) Make a longitudinal section of the 
end of a branch of the marine alga, Codium tomentosum. Here 
the growing region is not a few cells as in a true growing point, 
but each filament elongates at the apex without the production 
of cross walls. Many of the Red Seaweeds (Rhodophyceae) 
show the same type of apical growth except that transverse 
walls are formed near the apex of each filament (e.g. Melobesia, 
Nemalion, etc.). . 
(b) Examine the end of a shoot of Sphacelaria, one of the 
Brown Seaweeds. Here there is a single apical cell which divides . 
by a transverse partition, the segments thus formed dividing 
longitudinally and transversely. 
(c) Make a thin longitudinal section through the growing 
point of a moss or of a stem or root of a fern or horsetail 
