310 REPRODUCTION 



number of individuals in the same manner. Cut apart the sepa- 

 rate branches of a thallus of Marchantia, and place the fragments 

 on a layer of moist sand in a dish, covered with a glass plate to 

 form a moist chamber. Divide another plant into segments and 

 test the capacity of those from different parts of the thallus to 

 reproduce the entire individual. If antheridial or archegonal 

 branches are present treat these in the same manner. 1 



397. Propagation by Gemmae and Other Special Bodies. Uni- 

 cellular plants carry on multiplication by simple division and 

 fission, the simple cell becoming an adult individual before or 

 shortly after it is cut off. Species of greater complexity of struc- 

 ture separate masses of protoplasm for the purpose of effecting 

 reproduction, which in some instances differ but little from unicel- 

 lular spores. Such gemmae, or brood-bodies, may consist of 

 chains, plates, or globular cell masses containing a few, or hun- 

 dreds of cells. Gemmae are generally produced from the exter- 

 nal layers of the body, although instances are not wanting in 

 which they develop in the internal tissues. The formation of 

 gemmae may sometimes be induced by mutilations, and their 

 appearance is generally due to modifications in the external tro- 

 phic factors. 



Propagative bodies among the mosses are generally modified 

 leaves, stems, or antheridial branches, while the same purpose is 

 effected in the ferns, fern allies, and seed plants by buds devel- 

 oped in diverse ways. These may be considered with reference 

 to the part of the body from which they originate. 2 



398. Reproduction by Gemmae of Georgia (Tetraphis) pellucida. 

 Take up some decaying wood on which is growing Georgia pel- 

 lucida, in autumn or spring, and remove to a moist chamber in the 

 laboratory. Examine the cup-shaped receptacles at the ends of 

 the branches for gemmae. These are irregular, lens-shaped 

 bodies borne on stalks in place of antheridia among the para- 



1 Vochting, H. Ueber Regeneration der Marchantieen. Jahrb. Wiss. Bot. 16 : 

 367. 1885. 



2 Goebel, K. New formation of organs in regeneration. Organography of plants. 

 Parti., p. 44. 1900. 



