Formed Constituents of Organisms 167 



then that, Hke similar cells, it contains two or more ferments 

 for food transformation. 



As experiments in test-tubes and on live slides show, it ex- 

 hibits long-acquired and hereditarily fixed physiological re- 

 sponses to environal stimuli. Thus, when unilaterally illum- 

 inated by optimum intensity of white light in a small test 

 tube, it after being simultaneously stimulated by gravic action 

 and showing to this negative or apogeotropic response, by 

 oxygen and CO2 and showing positive chemptactic action, 

 exhibits no "trial and error" movement, but, after placing 

 itself so as to allow these stimuli jointly to act, starts, after 

 an excitation period, on a compounded line of movement that 

 is the resultant of the lines of stimulation that have acted on it. 

 But, should an intense light fall directly on the tube, the irritant 

 blue-violet rays start a paraheliotropic stimulus, and then a 

 line of movement is executed that is again a resultant pathway 

 representing the compounded action of all the stimuli alike 

 as to form and intensity of energy applied. Each stimulus 

 acts directly as in a sluggish vegetating acaryophytic alga, but 

 in this simple nucleated caryophyte all of the stimuli are linked 

 up or compounded so as to give a new resultant pathway (p. 129). 



If we suppose our unicellular Chlamydomonas then to undergo 

 gradual evolution, histologically and physiologically, into a 

 higher plant, the result would be, not the appearance of many 

 new morphological or physiological "characters" in the vaguely 

 understood sense of the word, but the septation or membering 

 of it into many cells, to one or to groups of which would be 

 allocated the "characters" and functions that existed together 

 in its unicellular state. Thus, as happens in the growth of 

 many multicellular algoid sporelings, the clear ciliary and fixing 

 end, becoming septated, might develop the rudiment of a 

 holdfast, and in still higher plants the rudiment of a root, that 

 would show restricted geotropic and apoheliotropic localization. 

 The green protoplasmic end, continuing to enlarge and septate, 

 might gradually withdraw the chloroi)hylloid substance into 

 the deeper placed cells, and thus the mass would originate a 

 colorless epidermis — rarely chloroi>hylloid in higher plants — 



