III. 



CONIFERAE. 



IN departing from the customary arrangement in the Natural System 

 and placing the Gymnosperms before the Vascular Cryptogams we have 

 been influenced chiefly by practical considerations, for the adoption of this 

 order will facilitate the discussion of the many doubtful forms which belong 

 to one or other of these classes, but which it will be best to consider in 

 connection with similar groups of Archegoniatae. 



Remains of Coniferae, branches, leaves, cones and seeds, are found 

 in great abundance in the Cainozoic and in the most recent of the Mesozoic 

 formations, and have been referred to genera still living on account of 

 their resemblance to them. Where such determination is based on well- 

 preserved cones, it may as a rule be considered satisfactory. Where the 

 cones are not in such good condition, we must keep in sight the possibility 

 of confounding them with cones and stems of Cycadeae. Where seeds 

 only have been preserved, the task is at once more difficult. Leaves and 

 leafy branches can be regarded by the botanist only in single exceptional 

 cases as a safe basis for the determination of genera or groups, for the 

 characters which they offer are few and not well marked, and the value 

 of these few must be regarded as doubtful when we remember that there 

 are recent genera from different families, in which the leafy branches cannot 

 be distinguished at all by the outward appearance and with difficulty even 

 by anatomical examination. Diselma Archeri, Hook, and Microcachrys 

 tetragona, Hook, are examples of such forms. How difficult it was 

 to combine the male and female specimens in these plants correctly is 

 shown by their peculiar synonymy. Nor must the heterophylly be for- 

 gotten, which prevails so widely in the Coniferae. We have only to think 

 of Juniperus virginiana, of Retinospora in the young states in the Cupres- 

 sineae, and of Glyptostrobus chinensis. Voltzia heterophylla, which will 

 be considered below, is an example of the same phenomenon in fossil forms, 

 as its name imports. Perfect certainty therefore in the determination of 

 branches of Coniferae can only be attained when we find them in con- 

 junction with cones in a satisfactory state of preservation. But in many 

 cases the two are not known in actual connection, being only associated 



