Facts relating to the Structure of Seedlings . 263 
It is a curious fact that Type 3, in a pure or modified form, is by far 
and away the most common mode of transition in the Phanerogams. The 
question naturally arises, Does not this indicate that the possibilities of 
evolving distinct methods of transition, especially in plants characterized by 
small seedlings, are so limited that but little, if any, reliance can be placed 
on such characters ? With regard to plants with large seedlings, the 
possibilities alluded to are greater, but, as will be seen later on, the 
anatomical features concerned are susceptible of being explained on purely 
physiological lines. 
Then there are various anomalies, more or less serious, which have to 
be explained away. For instance, the marked resemblance in the seedling 
anatomy of the Gnetales, Podocarpus and Araucaria ; the occurrence of the 
Anemarrhena type in the Ranunculaceae, 1 Cactaceae, 2 and Bignoniaceae ; 3 
and the resemblance between Ranunculaceae, Piperaceae, 4 and Araceae. 5 
Further, the differences between closely allied genera and species are not 
altogether convenient ; for example. Nopalea n. sp. and Opuntia Ficus -indie a 
or Opuntia albicans and Pereskia n. sp. appear, on the use of these characters, 
more closely related than Opuntia Ficus-indica and O. albicans. Then, 
again, the details are not always constant in a single species, e. g. Echinopsis 
multiplex , Pilocereus exerens , and Mamillaria rhodantha. If further instances 
be required, they will be found in Lee’s work on the Sympetalae ; this 
author shows that in the Personales, Polemoniales, and Lamiales the pre- 
vailing type of transition is Type 3, but in each of the groups Polemoniales 
and Personales a single natural order shows, in part, a different arrangement. 
That is to say, orders, e. g. Bignoniaceae, and even genera which are 
usually accepted as being allied show different methods of transition. 
1 Sargant, E. : Theory of the Origin of Monocotyledons founded on the Structure of their 
Seedlings. Ann. Bot., xvii, 1903. 
2 de Fraine, E. : Cactaceae, loc. cit. 
3 Lee, E. : Observations on the Seedling Anatomy of certain Sympetalae. Ann. Bot., xxvi, 
1912. 
4 Hill, T. G. : Piperales, loc. cit. 
6 This similarity of certain features of plants more or less widely separated is, of course, not 
restricted to vegetative features. Thus Church (Types of Floral Mechanism, Oxford, 1908) remarks 
that 1 the possession of a Mean Type of Flower by any plant cannot be regarded as a necessary mark 
of “affinity” with any other : it may represent a reduction-phase which maybe reached in many 
diverse phyla, and such forms would then resemble each other only by convergence of type ; the 
significance of this diagram being purely biological, in that it represents a certain balance between 
modern floral organizations and the external environment on which they are dependent for their 
successful development, protection, and pollination. On the other hand, it is equally possible to 
regard it as indicating a definite generalized biological stage in the main line of phylogenetic 
evolution on which different phyla have superimposed different secondary devices of their own. . . . 
The prevalence of this Mean Type Diagram throughout the modern flora is one of the remarkable 
features of the vegetable kingdom. It is characteristic in its pure form, or as readily recognizable 
derivatives, of 30,000 species of Dicotyledonous flowers, or about one-third of all the flowers known 
in the world at the present time.’ 
The parallel between Church’s Mean Type and Van Tieghem’s Third Type of transition is 
sufficiently striking to need no further comment. 
