Nature and development of plants . ked upon as male and female cells or gametesalthough in these simple plants there is no indication of sex thatwould enable us to recognize them as such. In the precedinggroups, multiplication in numbers or reproduction has been ef-fected by the division of the cells or by the formation of moreor less modified cells, termed spores. All such methods of re- DEVELOPMENT OF PLANTS 153 production are called asexual since but one cell is utilized in theprocess. In sexual reproduction a cell is formed by the unionof the contents of two cells. The nuclei and protoplas
Nature and development of plants . ked upon as male and female cells or gametesalthough in these simple plants there is no indication of sex thatwould enable us to recognize them as such. In the precedinggroups, multiplication in numbers or reproduction has been ef-fected by the division of the cells or by the formation of moreor less modified cells, termed spores. All such methods of re- DEVELOPMENT OF PLANTS 153 production are called asexual since but one cell is utilized in theprocess. In sexual reproduction a cell is formed by the unionof the contents of two cells. The nuclei and protoplasmic con-tents of each unite so completely that a cell with but one nucleusand protoplasmic contents results. These sexually producedcells are called gametospores because they are formed by theunion of two gametes and are capable of forming a new plantin the same way as do spores. We may distinguish the sporesderived from single cells as asexually formed spores or we maycall them simply spores, while the spores formed by the fusion. %.x B Fig. 99. Sexual reproduction of Pinnidaria: A, two diatoms envelopedin a mass of jelly. The valves have been thrown off and the contents ofeach diatom have divided into two sexual cells or gametes. B, the fusionof the gametes.—After Karsten. of the two cells or gametes may be termed sexually formed sporesor gametospores. Both kinds of spores are devices to enablethe plant to increase in number or to meet some other problemin life, such as conditions unfavorable for growth. The sporesare especially to be looked upon as devices to bring about arapid increase in the number of individuals while the gameto-spores more usually serve to carry the plant over periods ofdrought or extremes of temperature which would prove fatal tothe plant. For this reason the gametospores are often providedwith thick walls and dense cell contents which enable them to i54 CLASSIFICATION OF THE ALGAE remain in a dormant condition until conditions are favorable forgrowth
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