EMBRYOGENY OF THE PTERIDOPHYTES 673 



of the greatest nutritive supply and take a strong curvature, as in L. clavatum 

 (Fig. 1 86). In others, again, it may provide the basal part of the embryo 

 and root, without any swelling (Sel. spinulosa^ Fig. 190), or an haustorial 

 swelling may be formed, with convex curvature, on the side next to the 

 food supply (Sel. Martensii}. In embryos without suspensor the hypobasal 

 tier may maintain this same function, but it is usually only slightly enlarged 

 (Equisctum, Fig. 214; Fern, Fig. 15; Isoetes, Fig. 191; Ophioglossum vulgatum, 

 Fig. 260 bis; Botrychium Lunaria, Fig. 263). It would appear from the 

 inconstancy of their development, and their position in relation to their 

 obvious uses when present, that these haustorial growths are of the nature 

 of relatively late and direct adaptations at or near to the basal region of the 

 axis of the embryo, and it is significant that there is no special haustorial 

 growth in Lye. Selago or in Selag. spinulosa, both of them species believed to 

 be primitive types of their respective genera. 



The extra-prothallial swellings, of the nature of protocorms, differ in 

 origin and in function from the intra-prothallial haustoria (Figs. 101, 178, 

 1 88): they spring from the epibasal tier, and do not serve as suckers. 

 It has been argued at length above (p. 351, etc.) that there is good reason 

 to believe them to be secondary in their origin : however greatly these 

 gouty interludes may affect the form and appearance of the embryo, their 

 effect is temporary, and the shoot ultimately settles down into a normal 

 Lycopodinous type. If this view of the protocorm as a special secondary 

 development be accepted, then it may be put on one side as not directly 

 affecting the bearings which embryogeny may have on the theory of 

 origin of the shoot. 



The various types of embryogeny observed among Pteridophytes have 

 now been reviewed, and it remains to attempt to separate the characters 

 which are secondary, special, and fluctuating, from those which are primary 

 and constant, with a view to some general estimate of the embryogeny 

 as an aid to a morphological conception of the shoot. Following the 

 reasoning contained in the preceding pages, the occasional swellings of 

 the nature of a protocorm or of a haustorium, together with the curvatures 

 and distortions which these often produce, may be set aside as secondary ; 

 similarly, the precocious developments of root or of leaf, which sometimes 

 upset the balance of parts in the embryo, may be set aside as special 

 biological adaptations ; for even where a cotyledon or a root appears 

 early and anticipates apparently the other parts, still in all accurately 

 observed cases the relation of the axis to the primary segmentations is 

 found to be maintained. Further, the position of the first root is always 

 lateral ; its orientation and level of origin varies, as well as the time of 

 its appearance : these facts point to its being an accessory part upon the 

 embryonic body. The first foliar development is inconstant in position 

 and time and number of the leaves, but it is constant in the fact that 

 the protophylls are always lateral with respect to the point where the 

 axis will appear, and orientated with regard to it, so that more or less 



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