ZOOLOGY A.ND BOTANY, MICROSCOPY, ETC. 49 



Pinna-trace in Ferns.* — 11. C. Davie publishes an accounl of the 

 pinna-trace in the Ferns, lie briefly notices previous papers on the 

 subject. There are two types of pinna-trace departure — the marginal 

 and the extramarginal. 1. In the marginal type the first indication of 

 the preparation for the departure of the pinna-trace, as the leaf-trace is 

 followed up the petiole, is an extension of the mass of tracheides on the 

 adaxial side of the petiole. In Asplenium obtusatum, a typical example, 

 the two mas>es of xylera are curved in outline, the convex sides of the 

 curves being directed towards each other. The adaxial extremities of 

 these xylem masses become extended towards the adaxial corners of the 

 petiole. As the pinnre are not inserted exactly opposite to each other 

 first the extremity of one and then that of the other xylem-mass is 

 separated off from the parent trace. Phloem completely surrounds the 

 xylem in both portions of the leaf-trace, and the marginal tracheides 

 when nipped off are surrounded by a narrow ring of phloem. There are 

 protoxylem elements at the abaxial tips of the leaf -trace and on the 

 adaxial sides, not far from the ends. The pinna-trace has one small 

 protoxylem group on one side at the time of separation. As the 

 tracheides at the margin of the leaf-trace strand are separated from the 

 parent strand to supply the pinna-trace, this type of pinna supply is 

 termed marginal. 2. The extramarginal type differs in leaving the 

 leaf-trace margins intact throughout the petiole. In Didymochlsena 

 truncatula the leaf-trace i> composed of several strands. The two 

 adaxial strands have their margins sharply recurved, so that they are 

 almost parallel to the adaxial surface of the petiole. To supply the 

 basal pinna, the back of the hook is lengthened towards the adaxial 

 corner of the petiole. Across the narrow space between the two strips 

 of tracheidal tissue thus formed new tracheides spread. The original 

 outline of the leaf-trace strand is thus re-formed, while a ring of 

 tracheides is attached to the back of its hooked portion. This ring 

 soon separates, to pass into the base of the pinna and then divide up 

 into a pinna-trace resembling the leaf-trace. The margin of the parent 

 trace remains intact during the process. Since the pinna-trace goes off 

 from the outside of the parent strand, the method of supply is termed 

 extramarginal. 



Various modifications of these two types are described by the author ; 

 and he also gives a classified table of the results of his investigation. 

 This table is the subject of a detailed discussion in which a comparison 

 is made with the structure of the leaf -trace in fossil ferns. Further, 

 the relationship of the tracheidal tissue to the water-supply of the upper 

 part of the frond is discussed, together with the question why the 

 marginal type of pinna-trace is more prevalent than the other. 



Azolla filiculoides.t — W. H. Burred gives an account of the 

 morphology and development of Azollajiliculoides, and of its life-history 

 as studied in Norfolk. He has specially examined the conditions of 

 spore-germination — the requirements of moderate temperature, illumina- 

 tion, and aeration. He is strongly of opinion that the only species of 



* Trans. Rov. Soc. Edinburgh, 1. (1914) pp. 849-78 (3 pis. and figs.). 

 t Trans. Norfolk and Norwich Nat. Soc. ix. (1914) pp. 734-42 (1 pi.). 



Feb. nth, 1915 v. 



