1896-97-] THE GAMETOPHYTE OF BOTRYCHIUM VIRGINIANLM. 281 



its terminal meristem are elongated cells which, later, give rise to fibro- 

 vascular tissues. The cotyledon, c, is also for the first time visible, and 

 beside it is the stem-meristem, s. Below is the very massive foot,/; 

 Figure 50, lithographed from a photomicrograph, represents a still later 

 stage of development. Here the root is almost ready to burst the 

 calyptra, cal. The cotyledon is distinctly seen, and at this stage, for the 

 first time, covers over the stem-apex, which now lies on the side of a 

 transverse fissure. No vascular tissue appears till the root has grown to 

 a length varying from five to twenty millimetres, and has burst the 

 calyptra. The first tracheides arise in the proximal region of the root 

 after ft has emerged from the prothallium. Subsequently they make 

 their appearance in the cotyledon and the stem-axis. 



Before referring to the further developmental changes in the nascent 

 sporophyte, it will be well to consider an interesting abnormality. In 

 figure 5 1 is represented part of a prothallus in which tracheides are 

 present, near a region of superficial decay. The decayed spot probably 

 marks the position of an embryo which has been injured and in con- 

 sequence has rotted away, So far as I have been able to learn, by 

 reference to the literature on the subject, such prothallial tracheides are 

 the invariable accompaniment of apogamy. Their presence was first 

 described in connection with this phenomenon by Farlow^^ in the 

 apogamus prothallia of Pteris cretica. They have since been seen by 

 many observers under similar conditions. Lang^s has recently found 

 them in the interesting reduced, apogamous, sporangiferous sporophytes 

 o{ LastrcBa dilatata, Presl, var. Cristata gracilis, Roberts and Scolopendrium 

 vulgare, L., var. rainulosissiimiin, Woll. According to Bower, tracheides 

 also occur in the prothallia [endosperm] of certain Cycads. In view of 

 the recent discoveries of antherozoids in the pollen-tubes of this group, 

 it would be interesting to know if the Cycads also manifest the phenom- 

 enon of apogamy. 



The example figured is the only occurrence of prothallial tracheides 

 which has come under my notice in examining a large number of 

 gametophytes. In this case both antJicridia and archego^iia were 

 present. Recently an example of apogamy in Pteris aquilina has come 

 under my observation in which an apogamous and a normal embryo 

 were produced side by side on the same archegonial pad. The former 

 was accompanied by a single prothallial tracheid. The apparent rarity 

 of the phenomenon in Botrychiiini virginiiuiuni may be due to the con- 

 ditions under which the Metis specimens, which I have almost exclusively 



24. Quarterly Jourii;il ot Microscopical Science, vol. xiv., N.S., p. 266. 



25. Annals of Botany, vol. xi., pp. 157-168 ; also, Proc. of Royal Society of London. 



