FACTORS OF DECREASE 



127 



Arisantm, and in Najas, Caultma, can hardly be ascribed to any other 

 source than the fusion of the pollen-sacs, separate in the ancestry, into a 

 single loculus. Thus in the androecium of Angiosperms. and occasionally 









FIG. 69. 



Junipcrus cointmtnis. I., summit of a male flower seen from above. st\, the uppermost 

 staminal whorl of these stamens ; st. 2 , the second staminal whorl shows on each stamen 

 two pollen-sacs, and the indication of a lamina, /; s/ 3 , the third staminal whorl, of which 

 only the tips of the lamina? of two stamens are seen : each of the stamens of this whorl 

 had three pollen-sacs, not shown in the figure. II., the same in longitudinal section. 

 III., the same in transverse section. There is evidence here of reduction of the lamina, 

 and of fusion of the pollen-sacs. (After Goebel.) 



in the gynoecium, a fusion of sporangia is recognised, resulting in a reduc- 

 tion in their number. The apex of the male flower in Juniperus communis 

 has been quoted by Goebel as a probable example of fusion of pollen-sacs 

 (Fig. 69). In certain Pteridophytes the grouping of 

 the sporangia is often such as to suggest a previous 

 fusion ; but this has not been proved on developmental 

 pr comparative grounds for any one case, and the 

 question must be left open for discussion on grounds 

 of general probability whether the synangial state in 

 any individual case has been the result of fusion, or of 

 septation with incomplete separation of the sporangia : 

 obviously the synangial structure would be compatible 

 with either origin. Whatever the final decision for the 

 Pteridophyta may be, it is clear that fusion of sporangia 

 originally separate has actually occurred in Flowering 

 Plants : it is therefore a factor which must be regarded 

 as a possible explanation of all synangial states. 



(g) Abortion, partial or complete, of sporangia which 

 were fully matured in the type or ancestry is so common 

 a feature that special examples need hardly be quoted, 

 sacs are commonly found on staminodes, and abortive ovules are frequently 

 seen, as in Anemone (Fig. 70), which can only be accepted as the imperfect 

 representatives of a plurality of ovules in the ancestry. In the Pteridophytes 

 many examples of abortive sporangia have lately been described, and their 

 very important morphological bearings will be discussed at length in 

 Chapter XIII. But in connection with the circumstance that parts 



FIG. 70. 



Carpel of A nemone 

 nemorosa, L. Showing 

 one ovule developed, and 

 three abortive. (From 

 Engler and Prantl.) 



Abortive pollen- 



