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TEXTBOOK OF BOTANY 



61. The Cell (Fig. 14). — A cell of Spirogyra is longer than it is 

 wide, and cylindrical, like a length of stovepipe. The cells are joined 

 end to end, and the whole plant is surrounded by a continuous, rather 

 thick wall, which is made up of several layers. The outermost layer, 

 which is very transparent and therefore not easily seen, is composed 

 of a slimy substance, and it is this layer that gives to the plant its 

 slippery feeling. There are cross walls also between adjacent cells. 

 The most noticeable part of the cell is the green chloroplast. Each 

 chloroplast winds about spirally, within and close to the wall. There 

 are about one hundred known species of Spirogyra, and one of the 

 points of difference between species is the number of chloroplasts in 



each cell. Some species 

 have only one chloroplast, 

 some two, and some have 

 much larger numbers. Often 

 we find two or three species 

 mixed together, and it is 

 best to select for study a 

 form with one or two, or as 

 small a number of chloro- 

 plasts as can be found. 



The body of the chloro- 

 plast itself is distinct from 

 the coloring matter (the 

 chlorophyl) which makes it 

 appear green. This is shown 

 by the fact that the green 

 color can be dissolved out of the chloroplast by placing the plant in 

 alcohol. Scattered along the middle line of the chloroplast are a num- 

 ber of colorless pyrenoids. At just about the center of the cell is a 

 rather large, colorless, rounded nucleus. The nucleus is often hidden 

 by a coil of the chloroplast, but in some of the cells of a plant it can 

 usually be seen quite plainly if the microscope is carefully focused upon 

 the interior of the cell. In the nucleus there is a rounded body that 

 looks brighter than the rest of the nucleus ; this body is the nucleole. 



By careful study, one can see a thin layer of granular substance just 

 within the cell wall ; sometimes the layer is in active movement, as is 

 shown by the streaming of the granules that it contains. This layer 

 of granular material is a part of the slimy cytoplasm} Another layer 

 > Sometimes this slimy portion of the living matter of the cell is spoken of simply 

 as cytoplasm, or even as protoplasm. These terms are often confused ; but in the 

 usage of the most careful modern writers, protoplasm refers to all the substances 



be cd 



Fig. r4. — A single cell of a Spirogyra 

 plant; u, wall; b, outer layer of slimy cyto- 

 plasm; c, chloroplast, containing {i) pyre- 

 noids; e, nucleus, imbedded in a central 

 mass of slimy cytoplasm which is connected 

 by strands of the same substance with the 

 outer cytoplasmic layer. 



