232 



DE. AGNES AEBEE ON THE 



of tlie vascular bundle throughout tlie sporophyll pedicel. By their means, water could 

 easily pass from the sporophyll trace to the trabeculge. In Lepidostrohus oldham'ms 

 the sterile plates are best developed in the young sporangia whose spores have not com- 

 pleted their development, and in which the need, for the conduction of food and water 

 must be at its maximum (see PI. 24. fig. 15). 



In all the cases in IJepidosfrobus in which transfusion tracheides occur in the sporophyll, 

 these elements are noticeably abundant at the junction of limb and pedicel. Here they 

 are chiefly massed on the ventral side of the sporophyll trace, in the neighbourhood of the 

 ligule (cf. PL 26. figs. 41, 43, 44, 45). Among living plants we find an analogy for this 

 development of transfusion tissue in the tracheidal cup which surrounds the base of the 



ligule in Selaginella Icevigata, Baker, var.Xy«//n, Sp 



* 



Harvey Gibson has suggested f 



that the ligule in Selaginella is a mucilage organ, whose function is the temporary one 

 of keeping the growing point and young leaves moist. It seems quite possible that it 

 played the same part in the cones of Lepidostrohus^ and that, in both cases, the perform- 

 ance of this function is facilitated by the tracheides which occur in this region of the leaf. 

 The idea that the ofiice of the ligule may merely be to keep the delicate organs of the 

 developing cone from, desiccation, and that it is functionless when the fructification is 

 mature, gains some confirmation from Zeiller's % discovery that, in L. Browniif this 

 organ is quite ephemeral, and only survives in the young apical region of the petrified 

 cone. 



7. List oe Memoirs cited. 



13). — " On the Structure of Lepidostrohus laminatus, sp. nov." Rep. Brit. Assoc. Dundee, 



(1912) 



N 



"On the Fossil Flora of the Forest of Dean Coalfield (Gloucestershire), and 



West 



Wale 



}7 



Phil. Trans. 



(1912) 



W. ( 



Observations on the Structure of Fossil Plants found in the Carboniferous 



Strata. Part II. Lepidostrohus and some Allied Cones. Palaeontographical Society, London, 



1871, 



( 



(1893) 

 '94) 



1 



" On the Structure of the Axis o£ Lepidostrohus Brownii, Schpr." Ann. Bot. 



Morphology of Spore-producing Members. — Equisetineae and 



Lycopodinese." Phil. Trans. Roy. Soc. London, Ser. B, vol. 185. Pt. i. (1894) p. 473. 



( 



The Origin of a Land Flora. London^ 1908. 



Bbononiart, a. ('37).— Histoire des Vegetaux Fossiles. Vol. ii., 1837-38. 



Brown, R. ('48).—" Some Account of an undescribed Fossil Fruit.'* Ann. & Mag. Nat. Hist. 2nd ser. 



vol. i. (1848) p. 376.' 



Brown, R. ('51).— "Some Account of an undescribed Fossil Fruit." Trans. Linn. Soc. London, vol. xx. 



(18 



W 



p. 449, 



" An American Lepidostrohus," Bot. Gaz. vol. 11. (1911) 



* Gibson, R. J. H. ('96), pi. 8. fig. 21. 

 ZeiUer, R. ('11), pp. 33 & 34. 



t Gibson, R. J. H. ('96), p. 87 



