312 THE EMBRYO [CH. 



archegonial neck. He ascribes the difference to the early development of the 

 foot, which has brought about the change in position. He denies the fact 

 of an actual rotation of the embryo in the venter as suggested by Conway 

 Macmillan (257 bis) : and probably rightly. But in my view, all that is 

 necessary to effect the change is a swing of position of the first nuclear 

 spindle in the zygote. This would determine the plane of the basal wall so 

 that it should include the axis of the archegonium, instead of being at right 

 angles to it. In fact the initial polarity of the embryo would be altered, but 

 not the relative position of its parts. After this all would follow in the 

 normal course, and the relation of the cotyledon to the apex of the shoot 

 would remain unchanged. In either case the succession of parts as seen in 

 the median longitudinal section of the embryo reads thus : stem, leaf, root, 

 foot, but with the latter ill defined in the Marattiaceae and some others. 

 The Fig. 288 of HelmintJiostacJiys shows this relation of parts, as also do the 

 Figs. 294, b, c of Leptosporangiate Ferns. In other words, in the viega- 

 phyllotis Filicales the first leaf is on the same side of the axis-spindle as the 

 first root, a relation which is maintained in many Ferns in the adult state 

 (see Fig. 57). This fact bears physiological reasonableness on the face of it, 

 for it gives the shortest course for supplies from the root to the precocious 

 cotyledon. In microphyllous embryos, where its importance is less, this 

 relation is less constant. It may be noted that this relation accords with 

 Chauveaud's theory of the " Phyllorhize." 



Th.^ first root shows some variety not only in its point of origin, but also 

 in time : in Salvinia it may be absent altogether. But in point of orientation 

 its relation to the cotyledon is that above stated. In respect of time it is 

 usually complementary to the cotyledon : that is to say, when for purposes 

 of mycorhizic nutrition it is developed precociously, as in Botrychiuin Lmiaria 

 and Ophioglosswn zudgatjini, the cotyledon is usually delayed. But where 

 as in most Leptosporangiate Ferns the embryo is autotrophic, both advance 

 simultaneously. As regards the level of origin, the first root may spring 

 either from the epibasal or the hypobasal hemisphere. In all the Lepto- 

 sporangiate Ferns it is hypobasal, but in many of the Eusporangiates it is 

 definitely epibasal, Campbell remarks oi BotrycJiiuin virginiantun (255, p.48) 

 that " all the organs of the young sporophyte arise, as Jeffrey shdwed, from 

 the epibasal region, and in this respect B. virginiamim agrees with the 

 Marattiaceae and with Ophioglossumr Still several cases are left uncertain 

 by Campbell: nor is it of material importance that they should all be strictly 

 defined. The important point is that the root is not universally linked with 

 either hemisphere, but may be regarded as an accessory to the spindle-like 

 shoot, of various position and origin, and occasionally absent. In relatively 

 primitive Ferns it arises usually from the epibasal, but in the advanced 

 Leptosporangiate Ferns always from the hypobasal hemisphere. 



