Anatomie. — Biologie. 51 



with its two abaxial groups of protoxylem, exarch in position, and 

 two other widely separated lateral groups. 



The present author believes that this ingenious explanation of 

 the ph3'^logenetic origin of the trace of Lygodium is correct, except 

 that in it the adaxial hoops of the C-shaped trace are held to have 

 disappeared, whereas the French botanists believe that they have 

 become a constituent part of the solid, Condensed petiolar Strand of 

 Lygodium. 



In this connection Gwynne-Vaughan points out that the 

 young petioles of Lygodium scandens examin ed by him usually 

 contain onl}'' a single, abaxial protoxylem, which is apparently 

 sometimes mesarch in position. In L. japonicum the single abaxial 

 protoxylem is distinctly mesarch in position having a ring of cen- 

 trifugal xylem of its external side. The key to the problem, or 

 rather the proof of the theory, is held to be supplied by the struc- 

 ture of Davallia fumarioides. The petiolar bündle of the latter is at 

 first similar in structure so that of most of the ferns; higher up the 

 climbing habit, occurring also in the petioles of Lygodium., makes 

 itself feit. The leaf trace of Davallia fumarioides is at first an open 

 C-shaped bündle, with short stout adaxial hooks of xylem the ends 

 of which are thickened in a club-like manner. This bündle contains 

 shallow but distinct lateral bays and the abaxial part of the trace is 

 very narrow. As we pass up towards the region at which the 

 petiole assumes a climbing habit the trace closes up and becomes 

 reniform in transverse section. The Space between the two halves 

 of the xylem consists of pericycle and phloem. The former dis- 

 appears as the lateral xylem masses increase in bulk and the 

 phloem itself becomes reduced to a single row of sieve-tubes sepa- 

 rating the cells of the xylemsheath of each side. 



At the departure of a pinna- trace the protoxylem at the side 

 of the C from which the branch is about to depart divides twice and 

 the two outer protoxylems move out into the daughter-trace. If the 

 trace is a well-developed one the adaxial group of tracheides joins 

 up again with the main Strand before the branch trace is free; if 

 the daughter branch is a weak one the adaxial group of tracheides 

 may become free one or two inches before the departure of the 

 branch and not close up with the main Strand for a long time after 

 departure has been effected. After the junction the main branch 

 may appear to be temporarily mesarch for a short time. 



The pinna-trace is at first bluntly triangulär with two lateral 

 groups of protoxylem; a third dorsal, group appears later, formed 

 apparently de novo in a mesarch position. The adaxial xylem 

 parenchyma and phloem encroach on the tracheides and the xylem 

 thus becomes endarch and C-shaped. 



Isabel M. P. Browne (London). 



Scott, E. L,, A study of pasture trees and shrubbery. 

 (Bull. Torrey Bot. Club. XLII. p. 451—461. 13 text fig. 1915.) 



The haws, apples, oaks and elms are able to withstand constant 

 browsing by cattle for a prolonged period of time. 



In general other trees in pastures, as the ash, are killed within 

 a few years; or they are avoided by the cattle, as the hickories 

 and other nut-bearing trees. 



When the tree is able to withstand the cropping for a long 



