XLiv] BLECHNUM 167 



foliar gap a root-trace passes off: later the leaf-trace separates as two straps 

 which divide upwards into a varying number of strands, arranged in a horse- 

 shoe. This vascular system is of a type general for the genus; it is essentially 

 the same as in Matteuccia, but more subdivided. 



The fertile pinna of B. tabulare is typical of Loviaria, in that it has its 

 protective margins strongly curved downwards, and there is no flange. 

 A transverse section of a pinna of medium age appears as Fig. 690, 4, g. 

 The sorus which is continuous longitudinally is seated on the vascular 

 commissure here cut transversely. It is very perfectly protected by the 

 marginal flap, which is here unusually thick, doubtless as a xerophytic 

 adaptation. The succession of sporangia is gradate, a sequence rarely 

 departed from in this species : but one exceptional instance is seen in 

 Fig. 4, h. The question arises as to the relation of the flaps to the marginal 

 segmentation. Here, as also in B. discolor and other Lomarias, its origin is 

 marginal: but the relation to the marginal initial in any given section is 

 sometimes indeterminate, with a bias towards the concave side. Its origin is 

 clearly marginal in Fig. \,a,b: but the bias towards the concave side appears 

 in Fig. 4, c-f. This apparent variability may have its origin in differences of 

 the exact plane in which the selected sections were cut relatively to the 

 strongly circinate pinna. 



Blechnum lanceolatum (R. Br.) Sturm 



The same question arises also in B. lanceolatum (R. Br.) Sturm, a species which shows 

 no marked flange, though there may be a variable lateral distension of tissue. The outline 

 and venation of the fertile pinna are shown in Fig. 690, 5- Transverse sections at such a 

 point as {x-y) appear in outHne as in Fig. 690, 6, a. The indusial flaps are here thinner 

 than in B. tabulare, and the section is ahnost circular owing to distension of the tissues 

 below the receptacles, as photo-synthetic tracts bearing stomata. The commissure is as 

 before, but a vascular supply is often seen to branch off" towards the upper surface, each 

 twig of which terminates in a gland (e, b). The sporangia are here spread over a rather 

 wide flat surface, and with varying indications of a basipetal succession their order of 

 appearance graduates into a mixed state of the adult sorus. Usually the indusial flap springs 

 obviously from the marginal segmentation (6, d-f) : but if the section be cut near to either 

 limit of the soral region the flap may be replaced by another apparent margin, which a 

 reference to the basal part of Fig. 690, 5 will explain (e, £■). 



These two examples have been selected as showing the features typical of BlecAnum, 

 %Lo7naria. In the form and early development of the maturing pinnae there is a close 

 similarity in Blechnum, %Lomaria to what has been seen in Matteuccia (Fig. 683, D). In 

 neither is there any distinct "flange." The indusial flap appears itself to represent the 

 recurved margin, as it does in Matteuccia. Several other species suggest an intermediate 

 state leading towards the development of the flange as it is seen in Blechnum brasiliense. 

 For instance, B. attenuatum (Sw.) Mett., and B. LHerminieri (Bory) Mett., detailed de- 

 scriptions of which are given in Studies IV {Ann. of Bot. xxviil, 1914, PP- 377-379)- 



