‘ 
1 e : a oO ’ © 
ee ee / 
- 
_ + Wit 
‘ hh ie! 
‘a 2 v4 
side-walls (Figs. 71-74). 
-Fic.71.—Sieve-tube 
" from the white 
. bryony, Bryonia 
_. diotca, the horizon- 
__ tal_ partition-walls 
- with peculiar thick- 
“enings. ( X 250.) 
ze: 72.—Longitudinal section through 
4S , i. 
. ' ‘ 
‘ py a 
Sin i elt 
\ a : “ A me ! 
ee The Colas a Menther of a Group. 49 
~ and some have also sieve-like perforations through their 
Of similar construction are Zaf- 
the transverse partition-walls in the 
sieve-tubes of the gourd; Z the pri- 
mary cellulose-wall; % the second- 
ary cell-wall ; vw w the peculiar thick- 
ening which is always found in young 
cells ; z the contents contracted and 
passing through the perforations in 
tke transverse partition-wall. 
Fic. 73. — Transverse section of the 
same, the upper part represented 
with the thickening-substance which 
takes the form of wart-like eleva- 
tions; the lower part without it. 
(Strongly magnified.) 
E 
. m 4 
Wa eye : ieee, - z 
«<! / 
yi, f 
Fic. 74.— Part of a 
sleve-tube from the 
lime, 7zlia grandi- 
jfolia; p the sieve- 
discs of the radial side- 
wall. (<x about 800.) 
om tae 
