74 o THE POPULAR SCIENCE MONTHLY. 



modia a fact of great importance in its bearing on the phenomena of 

 inheritance. Recent researches, indeed, render it almost certain that 

 fertilization, whether in the animal or the vegetable kingdom, consists 

 essentially in the coalescence and consequent loss of individuality of 

 the protoplasmic contents of two cells. 



In by far the greater number of plants the protoplasm of most of 

 the cells which are exposed to the sunlight undergoes a curious and 

 important differentiation, part of it becoming separated from the re- 

 mainder in the form usually of green granules, known as chlorophyl- 

 granules. The chlorophyl-granules thus consist of true protoplasm, 

 their color being due to the presence of a green coloring matter, 

 which may be extracted, leaving behind the colorless protoplasmic 

 base. 



The coloring matter of chlorophyl presents under the spectroscope 

 a very characteristic spectrum. For our knowledge of its optical prop- 

 erties, on which time will not now permit me to dwell, we are mainly 

 indebted to the researches of your townsman, Dr. Sorby, who has made 

 these the subject of a series of elaborate investigations, which have 

 contributed largely to the advancement of an important department 

 of physical science. 



That the chlorophyl is a living substance, like the uncolored proto- 

 plasm of the cell, is sufficiently obvious. When once formed, the chlo- 

 rophyl-granule may grow by intussusception of nutriment to many 

 times its original size, and may multiply itself by division. 



To the presence of chlorophyl is due one of the most striking 

 aspects of external nature the green color of the vegetation which 

 clothes the surface of the earth : and with its formation is introduced 

 a function of fundamental importance in the economy of plants, for it 

 is on the cells which contain this substance that devolves the faculty 

 of decomposing carbonic acid. On this depends the assimilation of 

 plants, a process which becomes manifest externally by the exhalation 

 of oxygen. Now, it is under the influence of light on the chlorophyl- 

 containing cell that this evolution of oxygen is brought about. The 

 recent observations of Draper and of Pfeffer have shown that in this 

 action the solar spectrum is not equally effective in all its parts ; that 

 the yellow and least refrangible rays are those which act with most 

 intensity ; that the violent and other highly refrangible rays of the 

 visible spectrum take but a very subordinate part in assimilation ; and 

 that the invisible rays which lie beyond the violet are totally inopera- 

 tive. 



In almost every grain of chlorophyl one or more starch-granules 

 may be seen. This starch is chemically isomeric with the cellulose 

 cell-wall, with woody fiber, and other hard parts of plants, and is one 

 of the most important products of assimilation. When plants whose 

 chlorophyl contains starch are left for a sufficient time in darkness, 

 the starch is absorbed and completely disappears ; but when they 



