480 SECTIONAL TRANSACTIONS.—K. 
SECTION K.—BOTANY. 
Thursday, September 24. 
Prof. A. C. Sewarp, F.R.S.—A Contribution to the Karly History of the 
Lycopodiales. 
The paper deals generally with the history of the Lycopodiales, more especially 
with certain little-known Palzozoic genera from South Africa and the Belgian Congo. 
Attention is called to the occurrence in Devonian rocks of stems with leaf-scars 
apparently without any indication of leaf-traces. Reference is made to the 
geographical distribution of extinct Lycopodiales. 
Prof. J. H. Priestiry, D.S.0.—Phyllotaxis from the Standpoint of Develop- 
ment. 
Phyllotaxis is examined from the standpoint that the ordered succession of leaf | 
primordia at a growing shoot apex involves the mutual adjustment of a series of | 
successive ‘ growth-units,’ each unit consisting of a leaf and a portion of the subtending 
shoot axis. 
The first appearance of the primordium is to be traced to the relatively greater 
extension of the meristematic surface layer, as compared with the core of vacuolating, 
dividing tissue upon which it stands. These considerations attach importance to 
the procambial strands as regions of least transverse expansion, above which the 
superficial tissue will therefore be piled in a fold. In the Dicotyledon the folds thus 
produced undergo less horizontal expansion and give rise to ‘ sectorial ’ growth-units ; 
in the Monocotyledon they undergo extensive lateral expansion, and therefore 
completely surround the short apex, as peripheral or “holocyclic’ growth-units. This 
difference accounts for the different embryonic organisation which has provided the 
names for these two natural groups. 
Successive primordia are competing growth centres, therefore Hofmeister’s 
generalisation holds that each successive primordium tends to appear on the axis 
as far as possible from the preceding one. 
If no more than two primordia are growing at the apex, therefore, they tend to 
be opposite each other and the phyllotaxis, alternate and two-rowed. When more 
than two primordia are growing at once this position is impossible, and the angle of 
divergence between primordia is less than half of the circumference, but always tends 
to be more than one-third. Examined from this standpoint, if primordia appearin __ 
succession at equal intervals of time (the plastochrone), a spiral phyllotaxis system 
will result, in which the mutual adjustment of the successive growth units will lead 
naturally to the Fibonacci series of fractions to express the angular divergence. In 
this series, however, the ideal angle of divergence and the genetic spiral have no real 
significance, the governing developmental factors are Hofmeister’s rule and the need 
for lateral adjustments of sectorial growth units in the Dicotyledon ; peripheral or 
holocyclic growth-units in the Monocotyledon. 
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Prof. J. Dovie.—Some New Contributions to Conifer Morphology. 
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The structure of the Abietinean micropile, its manner of closure and the method : 
of pollination in the group have been less completely studied than other aspects of 
Abietinean morphology. The existing rather scattered records have been brought 
together and an endeavour made to complete them. The micropilar structure is 
definite and peculiar in each of the genera; it is never simply tubular as in other 
groups, and apparently no pollination drop occurs, the micropile having a stigmatic _ 
function. 
The other observations deal with the gametophyte and vegetative structure of 
some of the less-known Conifers: Fitzroya, Athrotaxis and Saxegothaea. 
The gametophytes and embryo of Fitzroya have been studied. It seems an 
interesting intermediate form between the Cupressoideae in the sense used by Saxton 
(Cupressineae of Seward) and the Callitroideae of Saxton (Callitrineae of Seward), 
its closest relation being with the latter. 
Some data on the unique development in Athrotaxis have already been published. 
The study of the genus has been continued. The archegonium, septate at the first 
