. Botany for agricultural students . Botany. 332 THALLOPHYTES Usually there is also a longitudinal line, which is a fissure or series of fine pores through which fine threads of protoplasm project and serve like cilia in locomotion. The halves of the box-like shell of a Diatom are called valves and the appearance of a Diatom depends much upon whether the face of the valve (the valve side), or the side showing the joining of the valves (the girdle side) is seen {Fig. 286). The protoplast usually has a large central vacuole with the nucleus suspended in the center by small strands of cytoplasm.
. Botany for agricultural students . Botany. 332 THALLOPHYTES Usually there is also a longitudinal line, which is a fissure or series of fine pores through which fine threads of protoplasm project and serve like cilia in locomotion. The halves of the box-like shell of a Diatom are called valves and the appearance of a Diatom depends much upon whether the face of the valve (the valve side), or the side showing the joining of the valves (the girdle side) is seen {Fig. 286). The protoplast usually has a large central vacuole with the nucleus suspended in the center by small strands of cytoplasm. Cell division is the chief method of repro- duction. The cell usually divides lengthwise and in such a way that the valves separate with the daughter protoplasts. Each daughter protoplast then develops a new valve on the naked side. In connection with this, a pecul- iar situation arises. The new valve de- veloped always fits within the old one and consequently there is a gradual reduction in the size of the individuals as division con- tinues, for at each division the daughter protoplast with the smaller valve is necessarily smaller than in the preceding division. How- ever, it has been found that the protoplasts shed their walls when reduction in size has reached a certain degree and in a naked condition grow to full size and then enclose themselves in new valves. This naked pro- toplast is called an auxospore (meaning en- larging spore). It is in connection with these naked proto- plasts that the sexual act occurs. Sometimes the protoplasts of contiguous cells conjugate and sometimes the four daughter protoplasts of two contiguous cells escape and conjugate in pairs. The zygospore usually enlarges and then encloses itself in valves. Thus Diatoms are one-celled and conjugate like some Green Algae, have the color of Brown Algae but have no zoospores or gametes like the Brown Algae. Stoneworts. — The Stoneworts constitute the group scientifi- cally known as the Charales. Some
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
