1386 



A TEXTBOOK OF THEORETICAL BOTANY 



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way to an understanding of what happened. The genus Thesium, in the 

 alhed family of Santalaceae, has a free-central placenta bearing three pen- 

 dent ovules, which are apparently naked 

 nucelli, or, as Fagerlind considers, ovules 

 with a single integument and an obsole- 

 scent nucellus of a few cells. In Santahim, 

 the ovules are fused into one structure 

 with the placenta (Fig. 1287). In most of 

 the Loranthaceae the fusion of structure 

 has gone further and the ovary is occupied 

 by a massive upgrowth, the mamelon, 

 embedded in which are the embryo sacs 

 without any recognizable ovular cover- 

 ings. In Viscum, the mamelon itself has 

 been reduced and is united to the base of 

 the ovary, the embryo sacs now appear- 

 ing to be embedded in the latter (Fig. 

 1288). Finally, in the extreme case, 

 Balanophora, the mamelon has been sup- 

 pressed and the single embryo sac is now 

 embedded in the swollen base of a cellular 

 structure, which extends upwards into an 

 elongated neck, the whole having a 

 striking resemblance to an archegonium, 

 except that there is no neck-canal. 

 Goebel and Fagerlind regard this as a 

 remarkably reduced carpel, the only 

 vestige of the female flower. Compara- 

 tive morphology supports this interpre- 

 tation, although Lotsy and others have 

 declared the structure to be a naked 

 nucellus. In some other genera of the 

 Balanophoraceae {e.g., Rhopalocnemis) the 

 male flowers retain a rudimentary perianth, which is wholly wanting in the 

 female flowers, even though their ovarial structure has not been reduced as 

 far as in Balanophora. It is therefore natural to expect the female flower 

 in the latter to consist of the gynoecium only, without any perianth. 



An approach to the condition in Balanophora is shown by Tupeia, one 

 of the Loranthaceae endemic to New Zealand. There is no ovarial cavity 

 and the archesporium lies at the base of a solid carpellary tissue, crowned 

 by a style and a rudimentary perianth. There is no doubt that in this 

 genus we have a reduced gynoecium and not an ovular structure. 



As in some few cases, mentioned above, vascular strands enter the in- 

 teguments and may even extend as far as the micropyle, so in some other 

 plants there is a vascular supply in the nucellus itself. The condition is, 

 however, rarer than vasculation of the integuments. In Myrica both types 



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Fig. 1287. — Santahim album. The 

 conical placenta with four emer- 

 gent embryo sacs growing upwards. 

 {From Griffiths," Trans. Linn. Soc", 

 1844.) 



