PROBLEM I. Hoiv Sh/iple Aui'/iials 



Fig. 364 The 

 lower side of a 

 SDiall piece of a 

 fern leaf. Ectch 

 dark spot contains 

 many tiny spore 

 cases. ]]'I.\it is in 

 the spore cases? 



( BROOKLYN BOTAN- 

 IC garden) 



this is going on, the end of the hypha 

 develops into a large ball or sphere 

 which is called a spore case (sporan- 

 ghnn). The spore case breaks open when 

 the spores are ripe and the spores are 

 scattered by movements of air. The 

 bread mold spores are so light when drv 

 that even slight movements of the air 

 carry them. The spores look colorless 

 when seen singly, but in a mass they ap- 

 pear black. 



Spore formation in other organisms. 

 Certain protozoa and a few of the simpler 

 invertebrates reproduce by spore forma- 

 tion too. It is an effective method, for 

 it provides very large numbers of off- 

 spring in a short time. While it is rare in 

 animals, it is found in many plants. 

 Spores are formed on the under side of 

 the caps of growing mushrooms, in lit- 

 tle capsules that grow on moss plants, 

 and on ferns. The lower side of a fern 

 frond (leaf) at certain seasons may be 

 marked with brown lines or dots. Out of 

 these you can shake a brown powder 

 which is a mass of spores. Tn ferns as in 



and Flams Reproduce 415 



molds only a small part of each plant 

 produces spores. 



A different type of reproduction. In 

 many simple animals and plants, repro- 

 duction is more complicated. Let us study 

 Spirogyra, one of many green pond 

 scums so common in slowly flowing 

 waters. See Figure 97, page 74. The 

 "scum" is a tangle of bright green 

 threads, or filaments, matted together. 

 Each thread is a separate plant. It is a 

 single row of cells, all alike in structure, 

 each of which can be seen through the 

 microscope to have a beautiful pattern 

 made by the chloroplast. 



If you collect Spirogyra in the spring 

 months you will have a good chance to 

 find it reproducing. If through the mi- 

 croscope you see two threads (filaments) 

 joined together you will know that re- 

 production is taking place. Let us study 

 it in detail. In each cell the spiral chloro- 

 plast (or chloroplasts) loses its shape and 

 the mass of cytoplasm begins to shrink 

 away from the cell wall. In the mean- 

 time, each cell sends out a projection to- 

 ward the cell opposite it in the neighbor- 

 ing filament. These projections continue 

 to grow toward one another. When they 

 meet, the cell walls dissolve at the point 

 of contact. This makes a continuous pas- 

 sageway or bridge from a cell of one fila- 

 ment to a cell of the opposite filament. 

 In other words, the cells of neighboring 

 filaments pair off with one another. 



When the bridge has been completed, 

 the protoplasm from one cell streams to 

 the opposite protoplasm which remains 

 stationary. Each cell mass of protoplasm 

 fuses with the one opposite, nucleus 

 uniting- with nucleus. The cells that fuse 

 are called gametes (gam'eats). Every 



