362 LYCOPODIALES 



Phlegmaria is believed to be primitive, the turgid developments of Z. 

 clavatum, cernuum and inundatnm, and also of Phylloglossum, are believed 

 to be secondary. 



The embryogeny of Selaginella (Fig. 190) corresponds in all essentials to 

 that of Lycopodium, and shows only minor distortion or swelling. In the 

 simple case of S. spinulosa the apex of the axis originates as before from 

 the centre of the upper tier : the active growth of the first leaf throws 

 the apex of the axis to one side ; but it is " righted " again on the 

 appearance of the second, and the identity of the apex is clearly 

 maintained throughout. The whole epibasal tier is then carried upwards 

 by intercalary growth of the hypobasal region, but the hypocotyl thus 

 formed is without lateral swelling, and the first root originates laterally 

 at its base. As regards distortions, this case is quite similar to that of 

 Z. Selago or Phlegmaria. But in other Selaginellas, as exemplified by 

 6". Martensii, the cotyledons arise equally, as indeed they sometimes 

 do in *$". spinulosa, and the temporary distortion of the apex does not 

 appear ; but a lateral swelling, absent in S. spinulosa, constitutes the 

 " foot." Thus Selaginella shows only minor and inconstant deviations 

 from the simple type. 



The embryogeny of Isoetes is less easily compared, but the following 

 tentative suggestion is given (Fig. 191). The suspensor is entirely absent, 

 and the embryo, composed only of the two tiers corresponding to those of 

 other Lycopods, is usually orientated so that its apex is from the first 

 directed towards the neck of the archegonium. That the rotation necessary 

 to bring this about may occur is indicated by the differences of position 

 of the basal wall noted by Campbell. The product of the hypobasal tier is 

 the haustorial foot only : the upper tier hastens at once to form the large 

 cotyledon, with the effect that the stem-apex is delayed, and remains 

 minute : it only becomes clearly recognisable after the appearance of the 

 second leaf opposite the first. In relative position, however, these parts of 

 the shoot correspond to those of S. spinulosa or Z. Phlegmaria. The 

 first root originates from the epibasal tier as in Lycopodium rather than 

 Selaginella, and unlike Z. Phlegmaria and S. spinulosa on the side opposite 

 to the cotyledon ; but the orientation of the root relatively to the cotyle- 

 don has been seen to vary within the Lycopodiales, so no great importance 

 need attach to this discrepancy. The primary embryogeny of Isoetes may 

 thus be held as related to that of the other Lycopodiales, but without a 

 suspensor, and greatly abbreviated, and with the apex of the axis correlatively 

 reduced and delayed in its development, owing to the early production of 

 the cotyledon and the root Nevertheless, its position at the centre of the 

 epibasal tier is maintained. 



It is thus seen that the embryos of all the Lycopodiales may be held 

 as variants on a single type, and fundamentally of spindle-like form. 



