247 
, 
The Classification of Conifers. 
the prothallus (as in Sequoia sempervirens) so that the mature 
archegonium is superficial; (ii) large numbers of archegonium 
initials may develop, as in Callitris and Actiuostrobus, of which only 
those in the neighbourhood of the pollen tube nuclei become mature, 
functional archegonia. 
Neglecting these differences, however, which only affect the 
present problem indirectly (e.g., as showing that the position of the 
archegonia is not primarily dependent on the position of the pollen 
tube) we can recognise in the main four types of arrangement of the 
archegonia in the prothallus. (I) Separate apical archegonia, each 
with its own jacket cells (where present), as found in Pinus, Sciadopitys, 
Taxus, Podocarpus, and many other genera. (II) Separate archegonia 
each with its own jacket cells (where present) hut not confined to 
the apex, as found in Araucaria and Agathis. (Ill) A group of apical 
archegonia, not separated from one another by jacket cells, but 
usually surrounded by a common layer of such cells, as in funiperus, 
Cryptomeria, Taxodiutn, Tetraclinis, and several other genera; in 
Cunninghamia a minor difference is met with, in the occurrence of 
a group of vegetative prothallial cells in the centre of the archegonial 
complex. (IV) One or (almost invariably) more lateral groups of 
archegonia, the individual archegonia not separated from one another 
by jacket cells as a rule, but the groups often surrounded by a 
common layer of such cells; occurs in Sequoia, Widdringtonia, 
Callitris and Actiuostrobus. 
As regards fertilization (number 10), there are three grades of 
size relation between the male and female nuclei (I) In Araucaria, 
Agathis, Sequoia, Widdringtonia, Callitris and Actiuostrobus the 
two nuclei are equal (or almost equal) in size. (II) In Pinus and 
Sciadopitys and several other genera usually associated with Pinus 
there is a very marked difference of size, the female nucleus being 
many times as large as the male. (Ill) In all other investigated 
genera there is a moderate difference in size, the volume ratio 
between male and female being about 1 : 3 or 4. In connection 
with fertilization it may be remarked that where an archegonial 
complex is found, the two male elements are invariably equal, and 
both are normally functional. Such characters are therefore 
evidently correlated with one another, and will not be further 
considered separately. 
The development and structure of the pro-embryo and early embryo 
must, in the writer’s opinion, be regarded as of primary importance ; 
in this respect, and neglecting minor variations, the following nine 
types may he distinguished. 
