3i6 



NATURE OF THE SPORANGIA 



from the mother cells as in the Bryophyta and are discharged 

 from the sporangia through a transverse cleft (Fig. 215, E). It 

 is interesting to note in a closely allied order occurring in the 



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Fig. 216. Cross-section of a stem of BotrycMum: p, pith; x, xylem; 

 m, medullary ray; c, cambium; ph, phloem; e, endodermis; cr, cortex. — 

 After Jeffrey. 



tropics, that the sporangia are developed directly upon the leaves 

 (Fig. 217) instead of upon special branches and that they are 

 sometimes associated together in groups, known as sori (sing. 



Fig. 217. Arrangement of the sporangia of an allied order, Marattiales; 

 A, leaflet of Archangiopteris with sporangia on surface of leaf and arranged 

 in groups or sori. B, magnified view of a portion of the leaflet. C, section 

 of leaf, showing two sporangia, the left-hand one in section. 



sorus) and provided with thickened cells, the annulus — charac- 

 ters that will become conspicuous in the next order. These 

 sporangia originate, however, as in Ophioglossum and open by 

 transverse clefts, which operation is promoted by the unequal 

 drying of the thick- and thin-walled cells of the annulate forms. 

 (a) The Gametophyte. — The gametophyte or sexual genera- 



