1907] BURTJNGAMESPORANGIUM OF OPHIOGLOSSALES 43 



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wall is very thin but distinct. Stevens reports the sporogcnous cells 

 of Botrychium as being devoid of a wall. The cells at this stage, in 

 the living condition, are probably still attached to one another so as to 

 form a compact tissue. In stained preparations clefts appear among 

 groups of cells. It is probable that some or all of these clefts arc the 

 effects of contraction in the preparation of the material. The nucleus 

 is usually quite round and is surrounded by a sharply defined nuclear 

 membrane. The nuclear network is not very unlike that of the cyto- 

 plasm, except that the beaded strands are larger, stain more deeply, 

 and present many more loose ends. From one to six nucleoli are 

 usually present in each nucleus. 



Whether the blocking of the sporogenous tissue begins as early as 

 the stage shown in fig. 8 or not, there is no doubt that it is clearly 

 present after the next division of the sporogenous cells. Such a 

 condition is shown in fig, 2, where the sporogenous tissue is seen to be 

 broken up into irregular blocks, and to be free from the tapetal cells, 

 which are beginning to separate from one another. Fig. j presents a 

 view of a slightly more advanced state of blocking. The irregularity 

 of Ophioglossum is in sharp contrast to the almost diagrammatically 

 regular blocking of the sporogenous tissue of Botrychium, According 

 to Cardiif, the division of the sporogenous tissue in that genus is in 

 three planes at right angles, and very regular and uniform in all parts 

 of the sporangium. He suggests that these walls break down in the 

 order of their formation, with the result that the tissue breaks up into 

 regular rectangular blocks. His figures lend considerable support to 



this view, and there seems to be no reason for doubting it. The 

 divisions in the sporogenous tissue of Ophioglossum are far less regu- 

 lar, and this may be the cause of the irregularity in the blocking. 

 Beer notes that the process in Helmlnthostachys is less regular than 

 in Botrychium. It is far more regular, however, than in Ophio- 

 glossum. An exceptionally regular case is shown in fig. 5. 



Correlated with the question of blocking is that of the division of 

 the sporogenous cells. In Botrychium, and to a less degree in 

 Helmlnthostachys, division is simultaneous in the sporogenous tissue 

 up to the time of blocking. After the blocks become independent, 

 the cells of each block divide simultaneously, but different blocks 

 may develop at different rates. Even so early as the stage shown 



