the Protein Bodies of Zea, Ricinus, and Conopholis . 361 
yet the possibility is not excluded that leucoplasts may elaborate bodies 
other than starch. All materials elaborated by plastids are derived pri- 
marily from the mineral salts taken from the soil and from the products 
of photosynthesis. Even in parasites devoid of chlorophyll, as Conopholis , 
where leucoplasts containing starch inclusions are present, the materials 
used by the leucoplasts came originally from the photosynthetic products 
of the host. 
In a voluminous publication, profusely illustrated, Guillermond (1919) 
endeavours to show that, in the cells of the flower of Iris germanica , 
Tidipa , and in flowers of some other plants, the pigments xanthophyll 
and carotin arise from plastids whose primordia are granular or rod-shaped 
bodies which can be recognized in the living cells with precision. 
Guilliermond (1920, 2) concludes furthermore that, in the epidermis 
of the young leaves of Iris germanica, vacuoles are formed by the hydration 
of a pre-existing substance in the cells in the form of mitochondria. This 
explanation as to the origin of vacuoles suggest the tonoplast theory. 
The earlier botanists, as Pfeffer. de Vries, and others, were inclined to 
look upon the cytoplasm., and the cell-sap especially, as a sort of mother 
fluid from which, with the exception of starch, reserve products, together 
with anthocyanin and the products of chromatophores, were separated as 
a physio-chemical precipitation. The trend of research at present is towards 
the view that these substances in the cell are the synthetic products ofperma- 
nent organs or plastids. These syntheses are, of course, supposed to be 
built up in accord with physical and chemical laws. A vital force is not 
assumed. But it is not admitted that these physio-chemical laws have been 
definitely formulated, in many instances at least. No one is prepared 
to tell us what chemical process is involved in the division of a chromosome 
or of a chloroplast. It has been seen that the function of a leucoplast may, 
under circumstances, be very similar to that of a chloroplast, and from the 
standpoint of function a leucoplast need not be greatly different from 
an oil plastid. The synthesis of starch and castor oil are processes that do 
not demand a widely different chemical activity, and it may not be bad 
chemistry to imagine that a leucoplast may, under certain circumstances, be 
able to synthesize castor oil as well as starch. 
Summary. 
In addition to leucoplasts and chloroplasts, protein and probably oil 
bodies owe their origin to plastids whose primordia are permanent organs 
of the cell, existing in the cytoplasm as densely staining rods or granules. 
In Zea Mays the primordia of the protein plastids are chiefly small 
rounded bodies distributed in the cytoplasm. These increase in size, 
becoming relatively large and very numerous, especially in the outermost 
layers of endosperm, the well-known aleurone layer. Small protein 
