SEA ANEMONES AND ALG 81 
believed to be part of the animal, and which puzzled 
naturalists because they contained chlorophyll, that 
remarkable green substance characteristic of plants, 
which gives to them the power of forming food out 
of its raw inorganic materials. These cells are now 
known to be minute seaweeds (Algz), which spend 
their lives in the animal tissues to the benefit of both 
organisms. The plant, by virtue of its chlorophyll, 
absorbs carbon dioxide, decomposes it, and gives out 
oxygen, which is eagerly seized on by the animal. 
The animal in its turn liberates carbon dioxide, which 
is required by the plant. Similar relations exist 
between Algz and some of the lowly Radiolarians 
and Foraminifera; in these cases, the animals being 
very minute, the plant partner plays a more con- 
spicuous role. It is noteworthy that these Algz are 
quite capable of living and multiplying separately, 
free from the body of the animals, and the animals also 
are capable of pursuing an independent existence. 
Let us turn now to the relations existing between 
flowers and insects, which form one of the most pic- 
turesque and romantic features of field life, and of 
which the materials for study and observation are 
ever at our own doors. What isa flower? A flower 
is a group of modified leaves set apart for the business 
of sexual reproduction. The essential parts or sporo- 
phylls are of two kinds, which may be borne on the 
same flower or on separate flowers on one plant, or 
on separate plants. These are the stamens, bearing 
pollen grains (or microspores), from which male cells 
arise; and carpels, which contain ovules, each enclos- 
ing an embryo sac or megaspore, in which is an ovum 
or female cell. 
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