Apical Growth in the Genus Trentepohlia. 247 
fit like an inverted bowl over the end of the cell, but often project 
from the extreme apex as an irregularly cylindrical stump. They 
often appear to grow for some time, and may attain a length of 40//.. 
(Fig. 6A). 
During the growth of the apical cell the osmotic pressure is 
considerable. The weakest part of the wall is the apical part 
immediately below the apical secretion of pectose, and normally 
this is the region of the cell-wall in which the successive cellulose 
lamellae become distended and gradually broken through. It 
happens frequently, however, that the weakest portion of the wall, 
and therefore the line of least resistance, becomes shifted laterally 
to some point below the apex, under which circumstances this 
point soon becomes apical in position and the former apex lateral. 
In this way an apical cap often becomes lateral, and as the apical 
cell grows it is left some distance behind the growing apex. If, on 
the division of the apical cell, the next transverse wall is above the 
place of attachment of the cap, the latter will be on the penultimate 
cell. During this time a new apical cap is formed, and a repetition 
of the process frequently results in filaments with several lateral 
excrescences, each of which was at one time an apical cap (Fig. 6C). 
Reagents and stains show that all these caps consist entirely of 
pectose. 
T. aurea var. lanosa Kiitz. In this variety the branches taper 
so that the apical cells are much narrower. The cell-walls are 
lamellose with more divergent lamellae. Apical caps narrow and 
not so well developed as in 7'. aurea type. 
T. abietina (Flot.) Hansg. In this smaller species the cell-walls 
are lamellose with divergent lamellae. The wall at the extreme tip 
of the apical cell is fairly thick and apical caps are developed only 
to a small extent. 
T. odorata. (Ag.) VVittr. The lamellae of the cell-walls are 
almost parallel to the long axis and for the most part extend round 
the apex of the apical cell. The apical caps, when present, are 
minute and rudimentary, and were only discerned by staining. 
T. villosa (Kiitz.) De Toni. The lamellae of the cell-walls are 
almost parallel. Rudimentary apical caps of minute size were 
sometimes present as in the preceding species. 
T. poly car pa Nees et Mont. The lamellae of the cell-walls are 
almost parallel. Extreme tip of apical cell relatively thin, with a 
thin apical cap only definitely evident on staining with chlor-zinc- 
iodine. 
