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General Biology 



fertilization because sperm must swim to the neck-canal and pass through 

 this into the venter. Here it enters the egg where the nuclei of sperm 

 and egg unite. The fertilized egg now divides by mitosis very rapidly, 

 and the upper cells form a large globular spore-case with a thick central 

 column within known as the columella. This is surrounded by a dome of 

 spores, around which the wall of the sporangium is formed. The spore- 

 case later pushes against the wall of the archegonium by enlarging. 

 The wall is then ruptured, the top portion remaining as the calyptra 

 ( ) (Fig. 119), while the spore-case later opens by 



means of a lid. The lower cells produced by the dividing oosperm 

 become a swollen foot, which is imbedded in the tissues below. It re- 

 mains connected with the spore-case by a short stalk. 



The structure, which thus develops from the fertilized egg-cell, is 

 called the sporophyte (Fig. 114) stage of sphagnum. In fact, all such 

 simple plants which develop spores are called sporophytes. 



Simultaneously with the maturing of the sporophyte, the apex of 

 the female branch elongates into a leafless stalk about half an inch or 

 more in length, known as the pseudopodium. It is supposed that the 

 reason that the pseudopodium and sporophyte grow thus simultane- 



Antheridium of Pteris (B.), showing wall Fi 2- 116 - Sphagnum sp. 



cells (a.), opening for escape of sperm mother 



cells (e.), escaped mother cells (c), sperms A., B., young protonemata; C, older pro- 

 free from mother cells (b.), showing spiral tonema with leafy bud, k.; r., marginal 

 and multiciliate character. (After Caldwell.) rhizoids. (After Campbell.) 



ously, is probably due to the fact that cells in the foot secrete a substance 

 which stimulates the cells to divide and enlarge, resulting finally in the 

 formation of the pseudopodium. The advantage the plant gains is that 

 the spore-case is raised to a higher plane, and it can thus throw its 

 spores much farther than would otherwise be the case. 



As Sphagnum possesses no chlorophyl, it does not manufacture its 

 own food and must, therefore, live on the absorption of food-matter from 

 the gamete plant through the foot. 



The spores themselves develop in the following manner (Fig. 

 115). In the spore-case the inner cells differentiate into two kinds, one 

 making up the larger portion of the tissues, and the other, larger and 

 richer in protoplasm, forming a dome of sporogenous or spore-forming 

 tissue near the upper wall. It is from this latter type of cell that the 

 spore-mother-cells are developed. 



