XIX 



DEVELOPMENT OF SPIKE 



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apex of the axis. The sheathing stipule which envelopes the growing point as well as all 

 the later leaves, is formed early : the spike appears above it in 

 a median position on the adaxial face of the leaf, but near to its 

 base (Fig. 363). The outgrowth soon becomes pointed and turns 

 upwards. It consists of a rounded outgrowth with a four-sided 

 pyramidal initial cell at the centre (".r" in Fig. 365, A, B, C, £), 

 but its identity appears to be soon lost, and the construction 

 passes over to that with four initials (Fig. 365, F, G). Con- 

 sequently the spike comes to be composed of four quarters 

 separated by walls at right angles, as seen in transverse section. 

 As the spike grows older a special band of cells, which may be 

 called the sporangiogenic band because it gives rise to the 

 sporangia, is developed running along the lateral margins of the 

 slightly flattened spike. It is derived from two regular rows of 

 cells which form part of the two abaxial quarters of the spike : 

 but usually the regularity of their arrangement is liable to inter- 

 ruptions. The sporangia formed from this band appear in con- 

 tinuous linear series : the details of their development are well 

 seen in the large spike of O.poidiilum (Figs. 366, 367). The cells 

 of the sporangiogenic band dividing periclinally and anticlinally, 

 certain cell-groups derived from the inner products soon begin 

 to show more dense protoplasmic contents. These are recognised 

 as sporogenous groups (Fig. 366, A^ B, C). The inner product 

 of the band is thus segregated into alternate blocks of sterile and fertile tissue. But the 

 whole of the cells of the sporogenous groups do not form spores : a peripheral part of each 

 group takes the character of a tapetum, and becomes disorganised as the development of the 

 spores proceeds. The outline of the sporogenous group that remains is very variable : but 

 when most regular it is as in Fig. 367, C, D, E. Meanwhile in the broad bands of sterile 

 tissue between the sporangia vascular bundles make their appearance, connected as branch- 

 bundles with the general system of the spike. The development of the spike in O. viilga- 

 tU7)i and reticulatum has been found to be essentially the same, though on a less bulky 

 scale. 



Fig- 363- 



vulmtum 



Ophiogloi,SH7n 

 The lower 

 drawing shows a longi- 

 tudinal median section 

 of a young leaf, with the 

 spike {sp) arising about 

 halfway up its adaxial 

 face. The upper drawing 

 shows a rather older leaf 

 in frontal view. ( x 35.) 



The structure of the sporangium of Ophioglossiun as it approaches the 

 stage of separation of the spore-mother-cells and of the tetrad-division, is 

 seen in Fig. 368. The tapetum, consisting of several ill-defined layers of cells, 

 becomes disorganised, its protoplasts fusing into a continuous plasmodium, 

 while the nuclei persist (Fig. 369). The sporogenous tissue breaks up into 

 packets, or finally into isolated cells, while the tapetal plasmodium penetrates 

 between them. Normally all the spore-mother-cells undergo tetrad division, 

 and form spores, though occasional cells may become disorganised {st. Fig. 

 369, A). When ripe each sporangium bursts by a horizontal slit, already 

 defined structurally in the tissue of the wall: it gapes as the tissues dry up, 

 but there is no mechanical annulus. 



The origin of the leaf in Botrydiiiim and of the fertile spike have been 

 described by Bruchmann for B. Lunaria {Flora, 1906, p. 213). He found the 

 spike to originate nearer the apex of the leaf than in OpJiioglossuni, probably 



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