132 



HUTCHINSON'S POPULAR BOTANY 



the giving off of oxygen in the manner described is not respiration. We 

 have been watching one of the consequences of assimilation. 



Mark, we say, ' ; consequences." The true act of assimilation in this 

 case the appropriation of carbon has taken place out of sight in the leaves, 

 which, as already stated, are the organs chiefly concerned in this important 

 function. The process itself is only imperfectly understood, though enough 

 has been discovered to stimulate inquiry. Undoubtedly the first stage in the 

 "building-up process is the union of C0 2 and H 2 to form the starting-point 

 for a carbo-hydrate ; and the first carbo-hydrate which can be detected in 

 the leaves is, as we have been pointing out, some form of sugar. The leaves 



are chemical laboratories, wherein 

 the little green corpuscles of proto- 

 plasmic matter produce results that 

 have baffled our Kolligers and Fara- 

 days, though every year the Plant 

 World is yielding up fresh secrets 

 to the patient workers of to-day. 

 The exceeding difficulty of the in- 

 vestigation may be gathered from a 

 remark by Mrs. Somerville, that 

 " although it may be inferred that 

 chemical action is the same within 

 the vegetable as it is in the inorganic 

 world, yet it is accomplished within 

 the plant under the control of the 

 occult principle of plant life." * 



Under certain conditions cells and 

 tissues containing chlorophyll have 

 their power of assimilation arrested 

 for a time, though the cells continue 

 to respire. Dr. A. J. Ewart has made 

 an extensive series of experiments 

 on various plants bearing upon this 

 point (see Journal of the Linnean 

 Society, vol. xxxi. pp. 364-461). The 



agents or circumstances producing this suspension of function are stated 

 by him to be " dry heat, moist heat, cold, desiccation, partial asphyxi- 

 ation, etherization, treatment with acids, alkalies, and antipyrin, accumu- 

 lation of the carbo-hydrate products of assimilation, immersed in very 

 strong plasmolytic solution, and prolonged insolation. The inability to 

 assimilate is, if the cell remain living, only temporary, being followed 

 sooner or later by a more or less complete recovery of the power of 

 assimilation." 



* Molecular and Microscopic, Science, vol. i. p. 168. 



FIG. 167. Bomarea carderi. 



Owing to a twisting of the leaf -stalk the lower surface of 

 the leaf is brought above, and the whole of the struc- 

 tural arrangements are altered to correspond with this 

 change of position. 



