162 Bulletin Jard, Bot. Buitenzorg, Série III, Vol. V. Livr. 2. 



The cytology of digestion. 



In physiological processes in animais or plants, chemical and mechanical 

 indicators are employed to help form a mental image of the process or 

 the results of a process. Thus efforts hâve been made to perfect self 

 recording devices for such purposes. The cytologist has tried to reconstruct 

 from his fixed and stained material the steps in a process; lie employs 

 his so-called stages as indicators. The steps in nutrition because they are 

 so difficult to record hâve left an open and rich field to the investigator. 

 Unfortunately the work that has been done in that field is yet meagre. 

 Sachs' work on germination is illuminating not only because it has ex- 

 plained the chemical processes involved, but also because he was able to 

 show, through the médium of the cells of the haustorium or scutellum and 

 the endosperm, the steps in the peculiar relationship between seedlingand 

 haustorium on the one hand, and the endosperm, the store-house offood, 

 on the other. 



The embryo" of Elaeis in the resting condition contains neither sugar 

 nor starch. If the embryo is examined directly after the fruit is ripe traces 

 of sugar and starch can be found. Thèse however disappear soon after. 

 The activities of the embryo before it is allowed to germinate are reduced 

 to the minimum. I hâve been able to prove to myself however that in the 

 so-called resting state of the "embryo some of the cell contents of the 

 endosperm tissue in the immédiate vicinity of the haustorium hâve been 

 used up. 



When germination sets in the embryo begins to expand so that it fits 

 siiugly in its cavity. The haustorium becomes active and attacks the sur- 

 rounding tissue. The cavity in such a stage, when the embryo has been 

 removed, shows the négative counterpart of the outlines of the haustorium. 

 On the other hand the haustorium and the embryo proper show the présence 

 of starch grains scattered throughout the tissue, however as we shall see, 

 with a definite kind of regularity. 



Before considering the further steps in the process, attention should 

 be called to the structure of the starch grains found in the cells of the 

 haustorium and embryo. The grains vary in size as we hâve seen in Figure 

 112, Plate XIll. In their gênerai structure they are oval or round. The hilum 

 is centrally located, usually it is tri-radiate — occasionally it is four radiate. 

 Surrounding the hilum is a halo whose radius does not exceed the radius 

 of the limbs of the hilum. The starch grains may or may not show con- 

 centric zones. The starch grains may appear singly or in units of two and 

 tliree. In such cases they become polygonal. When the. starch grains are 

 closely packed in a cell they become polyliedral (Figure 141, Plate XVII.) 



The structure of the cell walls of the endosperm tissue must be briefly 

 mentioned. The présence of primary membranes, used in the sensé that 

 Sachs has used the term, can readily be seen and also the thickenings 



