f 



MB. F. O. BOWEB ON APOSPORY IN PEEKS. 361 



The sori in Atliyrium Filix-fcemina, var. clarissima, appear in 

 the normal position with a normal indusium. In the condition in 

 which the specimens were when first I received them (Nov. 29), 

 the large majority of the sporangia presented an abnormal 

 appearance. Some few appeared of nearly normal structure, 

 with an annulus, but were arrested at a point of development 

 before the formation of the spores (Plate XI. fig. 1) ; others, and 

 indeed the majority of them, showed more or less distinctly the 

 central archespore, together with the cells which would normally 

 form the wall of the sporangium ; but there the normal develop- 

 ment seemed to have been suddenly arrested — the archespore had 

 not in these cases divided further to form either the tapetum or 

 the mother-cells of the spores (Plate XI. fig. 2). The arrest of 

 development of the archespore is, however, compensated in these 

 cases by the more active vegetative development of the stalk of 

 the sporangium and of the superficial cells of the head ; the result 

 being that the arrested sporangium ultimately appears as a club- 

 shaped body of larger size than the normal sporangium. The 

 individual cells also are of larger size ; they contain numerous 

 chlorophyll-granules which, if present at all in normal sporangia, 

 are relatively few in number. Further, the more rudimentary 

 the head of the sporangium is, the more marked is the vege- 

 tative development of the remaining parts. 



If pinnules showing the above characters be subjected to 

 favourable conditions of heat and moisture, the vegetative deve- 

 lopment of the sporangia may proceed at once. On pinnules 

 laid on damp soil, and forced quickly in the propagating-pits at 

 Kew, the earlier stages of this further development have been 

 traced. The details show great irregularity ; and they are found 

 to correspond to the greater or less completeness of arrest in 

 the normal development of the sporangium. Thus sporangia 

 which show a clearly marked annulus do not usually assume any 

 further vegetative activity ; those, however, which are arrested 

 at an earlier stage in their normal development may produce, by 

 a purely vegetative process, outgrowths of very irregular form. 

 Sometimes all the superficial cells of the club-shaped body may 

 take part in the process, and this is most clearly seen where the 

 arrest of the normal development is most complete (Plate XI. 

 fi g8. 3, 5, 6). In other cases the head of the arrested sporangium 

 may be thrown off, while the stalk continues its vegetative growth 

 (Plate XI. fig. 3). The result is in either case the formation 



