316 PRACTICAL COURSE IN BOTANY 
is the bubbles of gas that were seen rising in the liquid which 
cause beer to effervesce and bread to rise. They permeate 
the dough and by their expansion produce the sponginess 
peculiar to leavened bread. Look for a cell with a bud form- 
ing on it; from what part does it appear to grow? Wherea 
number of buds remain for some time attached to the mother 
cell (Fig. 449), they form a colony. Make a sketch of a 
single cell and of a colony of two or more adherent ones, 
labeling all the parts. If the cell wall cannot be made out 
clearly, run a little glycerine, or salt water, under the cover 
glass with a medicine dropper. What causes the contents of 
the cell to contract and leave the wall? (56, 59.) 
358. Reproduction. — From time to time buds break away 
from the mother cell and form new individuals or colonies 
of their own. ‘This process is called multiplication by bud- 
ding, and is only another form of cell division. 
Whenever reproduction takes place by other means than 
seeds or spores, it is said to be vegetative. This sort of repro- 
duction is not confined to unicellular plants, but exists also 
among the phanerogams, the propagation of species by means 
of buds, tubers, rootstocks, runners, grafting, and the like 
being variations of the same process. On the other hand, 
yeasts and bacteria and the unicellular alge have the power, 
under extreme conditions, to form resting spores, which 
sometimes lie dormant for years and resume their activity 
when favorable conditions return. 
Practical Questions 
1. When is fermentation useful to man? 
2. What is the effect on canned fruits and vegetables if yeast cells get 
into them? 
3. Why does milk turn sour in warm weather? (350, 351; Exp. 96.) 
4. Why do buttermilk and clabber spoil if left ‘standing too long? 
(345, 356.) 
5. What causes bread to be “heavy”? (356, 357.) 
6. Why will dough not rise unless kept in a warm place? (Exp. 96.) 
7. Why is beer kept cold during fermentation? (350, 356.) 
