34 
INDEX 
References are to pages 
Souring of milk, cause of . . 314 
Southern cattle tick . . . 460 
Spanish influenza.493 
Sparrow, chipping, useful bird 114 
example of bird. 9 
fox, example of transient bird 112 
hawk, destroyer of grass¬ 
hoppers .31 
destroyer of cicadas ... 34 
Sparrows, seed-eaters .... 117 
Spawn, migrations of fishes to . 76 
Spearmint, member of mint 
family.300 
Special modifications of plants 
356-372 
Special senses, organs of 75 
Specialized roots.252 
Specialized stems.263 
Speed a test of efficiency . . 477 
Sperm, cells of fishes .... 78 
cells of fern.336 
.nucleus of pollen grains . . 209 
of moss plant.329 
of volvox.153 
Spermaries of hydroids . . . 165 
Spermary of frog.87 
Sphinx moth from tomato 
worm 40 
Spicules, described .... 156 
Spider, member of Arachnida . 65 
Spinal column of man, curves of 434 
Spinal cord, part of nervous 
system.89 
Spines of echinoderms 169 
Spiracles, of grasshopper 22 
Spiral arrangement of scales on 
cones.343 
Spiral bands of chlorophyll in 
spirogyra.306 
Spirillum, a form of bacterium . 309 
Spirogyra, example of algae . . 304 
described.305 
reproduction of.306 
Spirogyra and pleurococcus, 
summary of.308 
Spleen of frog.87 ! 
Splints, use of in setting bones . 435 | 
Spoiling of food by bacteria 313 
Sponges, classified .... 8 
described.155 
discussed. 155-158 
Sponges — Continued 
economic importance of . . 157 
example of Porifera ... 8 
how gathered.158 
how prepared.158 
relation to other animals . . 158 
structure of.155 
summary of.158 
use of bacteria in preparation 
of.311 
where obtained.158 
Spongilla, reproduction of . 157 
Spongy layer of leaf .... 285 
tissue of velamens .... 373 
Sporangia, of ferns.334 
Spores, of bread mold . . . 325 
of club moss^ ..339 
of moss.328 
Sporophyte, dependence of . . 330 
generation of moss .... 330 
Sprain, defined.435 
Spraying to destroy insects . 43 
Spread of biological diseases 537 
Springs, source of water supply 463 
Spruce, a gymnosperm . . . 345 
example of gymnosperm . . 9 
Spur, part of flower .... 202 
Sputum, destruction of, neces¬ 
sary .490 
spread of tuberculosis by . 490 
Square stems of mint family . 300 
Squash, a dicotyledon . . . 227 
a fruit.245 
Squid, described.191 
example of cephalopods . . 191 
of mollusk.185 
Squirrels, damage done by . 135 
hinder reforestation . . . 357 
Stamens, described .... 198 
Staminate cones of pine . . . 343 
Staminate flower.203 
of monoecious plants . . . 204 
of willow.204 
Staminate strobili.343 
Starch, a nutrient.13 
chemical composition of . . 13 
form of carbohydrate . . . 416 
in cosmetics.504 
in flour.426 
Starfish, classified. 8 
described.169 
