394 SUMMARY OF CURRENT RESEARCHES RELATING TO 



are formed of narrow tabular amylaceous cells, and are in direct 

 connection with the placental tissue. The whole of the rest of the 

 tissue goes to the formation of the mucilage which brings about the 

 opening of the fructification. 



The tissue bounded by the lines of separation, which surrounds 

 the separate soral chambers, is sometimes termed in Marsilea the 

 indusium, a term which is correct physiologically, but not morpho- 

 logically. It is in the Marsileacefe formed by differentiation of 

 definite portions of the tissue of the leaf and the splitting up of these ; 

 and is not, as in the other Filicinefe, either a development of the 

 surface of the leaf or the recurved margin of the leaf itself. In the 

 pedicel of the young fructification is a vascular bundle, which 

 branches above into two arms ; in the mature organ are twelve 

 branches. 



The true position of the fructification has been a matter of con- 

 troversy. When mature it appears as if placed in the axil of a leaf 

 and independently of it. But that it is not in fact axillary is shown 

 by the presence in addition of a true axillary shoot, and also by the 

 structure of the vascular bundles. The examination of youug stages 

 shows clearly the foliar origin of the fructification. As in Marsilea, 

 the sori of Pilularia spring from the upper side of the fertile portion 

 of the leaf; as is shown by the position and structure of the pits. 



In all essential jDoints the origin of the macrosporangia and micro- 

 sporangia corresponds to that in Marsilea ; and the same is the case 

 with the origin of the sori ; in this respect the author differs from 

 Eussow's conclusions. The soral canal can be made out at the time 

 when the placenta is being formed, and is a direct continuation of the 

 pits. As in Marsilea the jjlacentEe are formed out of superficial cells 

 in depressions in the young fructification, corresponding to the structure 

 in the homosporous ferns and in Salviniacese. 



Aerial Branches of Psilotum.* — C. E. Bertrand divides the 

 aerial branches of adult Psilotum into the following classes, differing 

 in their morphological value : — (1) Aerial branches of the first order : 

 Cladode- or branch-stocks ; (2) Aerial branches of the second or a 

 higher order : Cladodes of the order in question ; (3) Terminal 

 branches or terminal cladodes ; (4) Simi)le aerial branches ; (5) 

 Sporangiferous branches or sporangiferous cladodes. 



Underground Branches of Psilotum.t — C. E. Bertrand states that 

 any transverse section of the median region of a simple underground 

 branch of adult Psilotum shows the following parts : — (1) A bicentral 

 slightly elliptical vascular bundle, the centre of which corresponds to 

 the centre of the section. (2) A protecting sheath surrounding the 

 bundle. (3) Between this sheath and the superficial layer a thick 

 zone of jirimary fundamental tissue, not differentiated into distinct 

 layers. (4) A superficial layer of epidermal cells, some of which are 

 prolonged into hairs, separated by a septum from the supporting cell. 



The structure of the vegetative tissue of a simple branch remains 



* Comptes Rendus, xcvi. (1883) pp. 390-2. 

 t Ibid., pp. 518-20. 



