CLASSIFICATION OF APPENDAGFS 145 



difficulties : of this the Psilotacea~e are a conspicuous example, and the 

 analysis of the parts composing their strobili has led to voluminous 

 discussions. The difficulties are no less in the Sphenophylls and Cala- 

 marians. The presumption upon which morphologists have habitually 

 proceeded has been that all the parts are, or at least should be, reducible 

 to certain categories, such as axis, leaf, emergence, sporangium these 

 being the headings under which the parts of the shoot in the higher 

 Vascular Plants are ranged. It is possible by the use of artifices, which 

 sometimes appear to be curiously strained, to carry out the classification 

 of all the constituent parts of the shoot in Phanerogams into these cate- 

 gories. But is the morphologist justified by this measure of success in 

 the practice of a somewhat artificial method in assuming that it shall 

 always be equally applicable to all Vascular Plants? And further, is it a 

 scientific method forcibly to extend the conclusions obtained from the 

 study of the higher forms to the lower? The attitude of the believer in 

 evolution should be the converse : to examine the lower types with a 

 mind untrammelled by conceptions derived from the higher, and a termin- 

 ology free to express what is actually seen in the more archaic forms. 

 Subsequently his conclusions may be extended to the higher forms. At 

 the present day it will seem hardly necessary to put down such simple 

 principles as these explicitly ; but doing so finds its justification in the 

 habit of thought, still ingrained in the science, of reading the lower Vascular 

 Plants in terms of the higher, just as it was done in the pre-Darwinian 

 days. From this the mind of the modern morphologist must be entirely 

 free. 



The difficulty of reducing the parts of the strobilus in certain Pteri- 

 dophytes to the categories above named has already extorted from 

 morphologists the adoption of a further term not yet used in reference to 

 Flowering Plants. The non-committing word " sporangiophore " is now 

 understood to connote a structure which bears sporangia, but is not readily 

 referable to the category either of axis or leaf, though it might be included 

 under some broad use of the term "emergence." It may contain vascular 

 tissue, and be inserted either on the axis or on an appendage. It will 

 be the object of this chapter to consider the relations of the sporangia, 

 the sporangiophores, and trie sporophylls to one another, and to the axis 

 of the whole strobilus, as seen in the various types of Pteridophytes. 



It is a rare thing for sporangia to be borne directly upon the axis 

 itself, though there is theoretically no reason against it, but rather the 

 reverse. The Lycopodiales include forms which show this position of the 

 sporangia, and Selaginella is usually quoted as a case in point (Fig. 74). 

 It is true that here the sporangium is inserted on the axis, and springs 

 directly from its tissue : it may originate as a swelling quite distinct from 

 that which develops into the sporophyll ; but the sporangia are not scattered 

 irregularly on the axis, for there is a constant relation of each sporangium 

 to the subtending appendage : the sporangium and the sporophyll are in 



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