130 W. l\I. Bale: 



hydrothecae in opposite pairs, and when l)i-anches are produced they 

 spring from below (or sometimes above) one of the paired hydro- 

 thecae. Thus there is no difference in the arrangement of the 

 ]iydrothecae on the stem and the branches, or as Nutting says we fin<l 

 "the stem and branches alike in every particulai." This is 

 obviously the simplest form of ramification possible, and is especi- 

 i\\\y found among the Diphnsine. Now, from this arrangement S. 

 .tenuis differs entirely, and, so far as the ramification is concerned 

 •(though not otherwise), it agrees with Schneider's " Thuiaria- 

 group," having each of the regular alternate pinnae springing from 

 below an axillary unpaired hydrotheca, while the stem-internode 

 supporting it supports also the normal pair, which in these circum- 

 stances are generally sub-alternate, the one on the same side as the 

 pinna being set higher up. The arrangement is exactly the same as in 

 .S'. marginata and niimerous larger species, such as 8. elongata, and 

 by its differentiation of the stem and pinnae is of a more advanced 

 type than that of .S". ;/rac/l/s. Besides the distinction Ijetween the three- 

 celled internodes of the stem and the tAvo-celled ones of the pinnae, 

 there is the further difference that the hydrothecae of the stem are 

 more divergent than those of the pinnae. Yet another distinction 

 which has been overlooked is that S. grdciJis has the nodes at 

 <listant and irregular intervals, while S. feni/is has them below 

 «very pair of hydrothecae (or every three hydi-otliecae in the case 

 of the stem). Some species, however, are said to vary in this 

 particular, and -S'. tenuis may possibly do so. but I have seen no 

 instances, except in the special cases mentioned Vjelow. 



While the pinnae, when present, are usually regular and alternate, 

 the habit is not so firmly established as to preclude the occurrence 

 of frequent irregularities. Thus it is not unusual to find the two 

 lowest pinnae of a shoot on one internode and opposite (a condi- 

 tion, it may be remarked, which occasionally occurs in several other 

 small alternately-branched species, both of Sertiilar/(i and Phnnii- 

 laria). The internode thus bears four hydrothecae. the two axillaiy 

 ones and the regular pair, which are now opposite. Even on a 

 pinnate stem there may bo intercalated between two pinna-bearing 

 internodes an intoi-nodi- sujtjKuting (inly a ])air «>t' hydiothecae. It 

 is usual for the four or five intei-nodos at the top i>f a pijinate stem 

 to bear hydrothecae only, in which rase tliis portion entirely 

 resembles a pinna, the hydrothecae being ojijiositc and becoming* 

 less divergent towards the summit, 'i'lu- sini)))*' slioots. which are 

 the most numerous, have ri'gular t \vo-rfll('(l internodes, Imt tlie 

 hydrothecae (except at ihe to]») are widelv diveigent. like tliose 



