204 
James Small. 
Fossil Composites. A list is given of most, if not all, known 
fossil Composite. The occurrence of the various types of fossil 
Composite fruits is shown to be in accordance with the phyletic 
suggestions in previous chapters. 
Cytology. Considering relationships within the family, the 
chromosome number is shown to be of some phyletic value. The 
development and type of haustorial antipodals also agree with 
previous phyletic suggestions. 
Latex. A general theory is given of the evolution and functions 
of laticiferous tissues; the functions are excretory and nutritive; 
the evolution is suggested to be the result of epharmonic adapta¬ 
tion to a climbing or rapidly-elongating habit, which requires the 
easy and rapid translocation of food materials obtained by the 
development of a laticiferous system. 
These are the general results, as distinguished from the 
phyletic results, which will now be discussed for each tribe. 
Phylhtic Conclusions. 
Senecionece. The main thesis of the preceding chapters is that 
Senecio was the first genus of the Compositae to come into existence 
and that it has directly or indirectly given rise to all the other 
genera of the family. That Senecio is the basal genus of the 
Compositae is a theory which is supported by all the details of its 
vegetative and floral morphology, physiology and cytology, i.e., 
the chromosome number, the antipodal haustorium, the anomalous 
septa and lateral placentae in the ovary, the simple structure of 
the seed and seedling, the simple appendages of the styles and 
stamens, the simplicity of the pollen-presentation mechanism as a 
whole, the simple type of irritability of that mechanism, the 
numerous species and varieties with discoid capitula, the variation 
in form, development, colour and vascular anatomy of the corolla, 
the setose-scabrid pappus, the pulvinate achenial hairs, the small, 
flat, simple receptacle, the uniseriate pericline, the slightly devel¬ 
oped calyculus, the alternate phyllotaxis of the cauline leaves, the 
development and contents of the secretory system, and the 
extreme plasticity of vegetative organisation or low physiological 
differentiation as shown by the marked response to a variety of 
ecological conditions. This theory is also confirmed by the 
geographical distribution of the genus and its close approach in the 
details of floral structure to the ancestral genera in the Lobelioidese. 
The 2500 species of Senecio, constituting 10% of the Composite, 
form a very substantial “trunk ” for the family tree (Fig. 79). 
