LYCOPODIUM. SPOROPHORE. 185 



Examine a good section of a sporangium under a high 

 power; the wall will then be seen to be of approxi- 

 mately uniform thickness throughout, and consists of 



a. A well-marked outer layer of cells of considerable 

 size. 



b. An inner ill-defined band, consisting of the remains 

 of disorganised cells. 



If the wall be observed in surface view the cells will 

 be seen to be of sinuous outline, and somewhat 

 elongated, with the exception of a zone which indicates 

 the line of ultimate dehiscence of the sporangium : 

 here the cells are shorter, and the walls are straight. 

 The line of dehiscence may also be recognised in the 

 wall as seen in section. Note also the structure of the 

 Spores ; they have the form of a rounded tetrahedron, 

 and the outer wall is covered with peg-like projections. 



By cutting similar median longitudinal sections of cones in 

 various stages of development, and comparing them, the history 

 of development of the sporangium may be traced. It may be 

 seen that the sporangium arises as a multicellular outgrowth of 

 the upper surface of the leaf ; at an early stage the archesporium 

 may be recognised as a hypodermal cell, or possibly several cells : 

 the superficial layer of cells above it gives rise by division to 

 three layers ; of these the innermost is the tapetum, which, 

 together with the next outer layer, is disorganised as develop- 

 ment proceeds, while the outermost layer is still persistent in the 

 mature sporangium. The archesporium meanwhile divides to 

 form numerous spore-mother-cells, each of which divides 

 tetrahedrally, and gives rise to four spores. 



The proper conditions for germination of the spores 

 of our native species not having as yet been discovered, 

 reference should be made to the Text-books for further 

 information as to the life-history of Lycopodium. 



