SYMBIOLOGY — THE BIOLOGICAL RELATIONSHIPS OF ORGANISMS 133 



are formed sparingly, or at least they do not develop to larger size in con- 

 siderable numbers. Due to the action of certain stimuli they may develop 

 very rapidly in large numbers, forming a new or an additional tissue iden- 

 tical with or very closely similar to the tissue from which they had their 

 origin. In other words sphaerocytes may give rise to a neoplasmic growth, 

 of which the mucilaginous layer enclosing the seed of the tomato is a 

 striking example. 



The following different kinds of sphasrocytes may be recognized in the 

 tomato. These are, in all probability, different stages in the development 

 of a sphaerocyte. 



a. Leuco-sphcsrocytes. — These are the youngest and earliest stages in 

 the development of sphaerocytes, as has already been explained. They 

 usually range from one micron to about six microns in diameter. 



b. Amebo-spkarocytes. — These resemble the leuco-sphserocytes in that 

 they are colorless and contain vacuoles. They differ in that they are al- 

 ways irregular in form and show a very slow to a rather marked ameboid 

 movement, resembHng the motion of the leucocytes of the blood and of 

 true amebae. The plasmic contents are more distinctly granular than 

 that of the leuco-sphaerocytes and the vacuolesare generally fewer, usually 

 from one to three. They resemble amebae excepting that there is no 

 distinct hyaloplasm (ectoplasm). In the ripe tomato these bodies are 

 few in number but in the green tomato they are quite numerous and show 

 very marked ameboid movement. They vary from 15 to 30 microns in 

 diameter. Most of them contain chlorophyll, from three to twenty or 

 even more unchanged chlorophyll granules of the same type and kind as 

 occur in the normal peripheral pulp cells of the green tomato. They 

 encyst quite readily and in this form they cannot be distinguished from the 

 larger leuco-sphaerocytes, especially those which are free from chlorophyll 

 granules. Since these actively motile cells occur in the intact fruit tissues, 

 especially abundant in the mucilaginous layer of the tomato seed, it is 

 reasonable to assume that they are derived from the plasmic elements of 

 the tomato itself and are not true amebae which might have entered from 

 the outside. Perhaps 10 per cent, of the total number of the sphaerocytes 

 are of the ameboid type and about 70 per cent, of these contain chloro- 

 phyll. There are indications that all of the sphaerocytes pass through the 

 ameboid stage. 



What analogy there may exist between the amebo-sphaerocytes of the 

 tomato and the amebocy tes of the Spongilla group is not determined. The 

 sponge amebocytes which are said to arise from the archeocytes are capa- 

 ble of ameboid movement and will form into new sponge cell aggregates. 

 That the amebo-sphaerocytes of the tomato are capable of multiplying by 

 septation is probable and that they may form new tissue cell aggregates 



