n6 THE POLYSPORANGIATE STATE 



cases while starvation may conduce to early flowering in many Angiosperms. 

 Thus the relation of nutrition to the production of sporangia is not of a 

 simple character. Goebel (Organography, p. 498) speaks of other factors, 

 such as intensity of light, and internal conditions or correlations, as 

 influencing the production of sporophylls. Experimentally it seems easier, 

 however, to convert sporophylls into foliage leaves than to make foliage 

 leaves fertile. He quotes, nevertheless, the case of a Fern, allied to 

 Acrostichum Blumeanum^ in which an arrest of growth of the rhizome, 

 after previous good nourishment, led to production of sporangia. This is 

 a result similar to that following root-pruning of fruit-trees. It reminds 

 us also of the conditions found by Klebs to determine the production of 

 reproductive organs in certain Algae and Fungi.' 2 I do not suppose, 

 however, that the conditions will be found to be uniform for all sporophytes, 

 any more than they have been for Algae or Fungi. In any case, the 

 present knowledge of the whole subject for Vascular Plants is indefinite 

 and uncertain. 3 



The time of distinctive development of cells as sporogenous cells varies 

 in different plants : the following tentative conclusions may be drawn from 

 such differences. When in a tissue-tract the distinction between vegetative 

 and sporogenous cells takes place relatively late in the individual, the 

 presumption is that the distinction has been of late origin in the race. 

 On this basis the conclusion has been founded in certain cases that increase 

 in number of sporangia by septation has occurred. A large potential 

 sporogenous tissue having a common origin is first seen ; but later it 

 differentiates, part becoming actually sporogenous, part remaining sterile. 

 It is concluded that these late-differentiated sterile tracts were once in 

 the race fertile, and that they were subsequently diverted from this previous 

 condition ; in fact, that the ontogenetic development reflects the evolutionary 

 history. This is exemplified in certain Angiospermic anthers, in the 

 synangia of Tmesipteris, and in the partially septate sporangia of Danaea-. 

 the same general argument holds also for the sporangium of Isoetes with 

 its trabeculae. In other cases where the distinctive characters of the 

 sporogenous cells or cell-groups are acquired earlier, the argument for 

 septation is less clear, though on grounds of comparison a similar history 

 of the structure actually seen appears probable. 



The cases above mentioned involve sporangia which are closely associated 

 as synangia, and they are naturally initiated simultaneously. But differences 

 of the time of distinctive development of sporogenous cells may become 

 more obvious in sporangia which are separate from one another, though 

 in close proximity upon the part which bears them. In those types which 

 comparison, as well as the Palaeontological record, points out as the 



1 Raciborski, Flora, 1900, p. 25. 2 Die Bedingungen der Fortpjlanzittig, 1896. 



3 The determining conditions have been discussed by various writers. See Uiels, 

 Jngendformen und Blutenreife iin Pflanzenreich, Berlin, 1906, where reference is made 

 to the literature on the subject. 



