40 



FUNDAMENTALS OF CYTOLOGY 



aspects presented by vacuoles in their various stages of development ma}- 

 be strikingly like those of the Golgi material in animal cells. That both 

 are involved in secretory activity is also suggestive. It is true that 

 plastids, too, when similarly treated, often show a strong resemblance 

 to the Golgi material. In the sperm-forming cells of mosses there is not 

 only a likeness in form and stainability, but a mass of material arising 

 from the plastid performs the same peculiar function as does a product of 

 the Golgi material in animal spermatogenesis (page 121). This would 

 seem to be a stronger argument for homology. A third constituent of 



Fig. 29. — The relation of the Golgi apparatus to secretion. 1—5, formation of secretory 

 droplets in goblet cell in intestine; 6, secretory globules with attached bits of Golgi material 

 from pancreas. {After R. H. Bowen.) 



plant cells, the so-called osynio-pkilic 'platelets, has been brought into the 

 controversy. 



An interesting light on this question has come from bean root cells 

 subjected to very high centrifugal forces — 400,000 times gravity for 15 to 

 20 minutes. In cells thus treated the cell constituents become arranged 

 in order of their relative specific gravity as shown in Fig. 30. It is to be 

 noted that the plastids and chondriosomes are relatively heavy, whereas 

 the osmiophilic platelets are relatively light, just as the Golgi material is 

 shown to be in animal cells similarly treated. 



Animals and plants have been going their separate ways in evolu- 

 tionary specialization for a very long time, the differences in nutrition 

 and cytological structure having become great enough to enjoin caution 

 in the drawing of homologies. We shall nevertheless continue to be 



