VEGETATIVE REPRODUCTION. 



215 



309. Food. — In almost all cases there is a suppl)- of reserve 

 food within the spore. This reserve food varies in amount 

 with the conditions under which the spores are formed. It 

 is ordinarily greater in resting spores than in those intended 

 for immediate growth. Spores may contain chlorophyll, but 

 generally do not ; even the spores of green plants are mostly 

 without it. Its presence seems to indicate an active condition 

 of the protoplasm, and the vitality of such spores is usually 

 of short duration. It is of course absent from the spores of 

 colorless plants, such as the fungi. 



Fig. 210. — Part of a vertical section of a leaf of a u-illow, attacked by a fungus {Melamfi- 

 sora salicina). eo, epidermis of upper side lifted by the young teleuto spores; t, de- 

 veloping from the spore-bed abo\'e the ends of the palisade parenchyma, /;;?- ,■ t-w, 

 epidermis of the under side, broken through spore-bed from which spring uredo- 

 spores, St. and paraphyses, /, eo will also finally be ruptured to set free /. Magni- 

 fied 260 diam. — .After Pranll. 



310. Growth. — Spores germinate by absorbing water, thus 

 bursting the more rigid layer or layers of the cell-wall. The 

 inner layer then grows in area to accommodate the increas- 

 ing protoplasm, which so controls the regions of growth and 

 the mode of cell division as to produce a plant of definite 



