'j6% GENERAL CONDITIONS OF PLANT-LIFE. 



observation shows that it is not the rays absorbed by the green colouring matter that 

 perform this woric either in the solution or in the living plant *. 



The Relation of Cell-division to Light has, as I have already explained, been completely 

 misunderstood by Famintzin. In my paper ' On the influence of daylight on the 

 formation and unfolding of various organs of plants' (Bot. Zeit. 1863, Supplement) 

 I described in detail a long series of phenomena which show that the fresh formation 

 of parts connected with cell-division is in general independent of light as long as 

 there is a supply of reserve food-material to support growth. The main results were 

 again collected in my 'Handbook of Experimental Physiology,' p. 31, referring also 

 to that paper. Notwithstanding this, Famintzin ^ commences his paper quoted above 

 (three years later than one, and five than the other of my works) with the words : 

 'The action of light on cell-division has not yet been carefully examined by any 

 one. All that I have been able to find on this subject is limited to a remark of 

 A. Braun's on Spirogyra and a statement of Sachs relating to cell-division in general.' 

 He then quotes a passage from Braun cited also by me, and continues : — ' Basing his 

 remarks on these statements, Sachs expresses himself as follows,' and then quotes 

 some passages from my Handbook, p. 31, no reference being made to the earlier 

 paper or its conclusions. He then maintains that his own observations lead to entirely 

 different results ; but it is easy to show that they rather lead to the same as mine. 

 At the end of his memoir (p. 28) he says: — 'The cell-division of Spirogyra is not 

 prevented by light, as has hitherto been supposed, but on the contrary is promoted 

 by it ' (which is incorrect). According to Famintzin's observations, this acceleration of 

 cell-division by light depends on the fact that light induces the assimilation of food- 

 material ; which is obviously a different question from that argued by me and opposed 

 by him ; since, presupposing the presence of a supply of food-material, I only argued 

 the question whether light exerts any influence on the physical fact of cell-division. 



' The cell-division of Spirogyra,' continues Famintzin, ' has been proved to be de- 

 pendent on light to the same extent as the formation of starch ; but the relationship 

 in the former case diff'ers from that in the latter in the following respect : — the formation 

 of starch is induced by a very brief exposure to light (about half an hour) and requires 

 that its action be direct; starch is formed only under the influence of light; in its 

 absence the formation at once ceases. Cell-division, on the other hand, is induced 

 only after light has acted for some hours ; it then commences in the cells whether 

 these are exposed to light for a longer time or are removed into the dark.' This 

 shows therefore that when food-materials are formed cell-division takes place in the 

 light as in the dark ; a fact which I had proved five years before by a greater number 

 of observations. 



Better in more than one respect is Batalin's treatise ' On the action of light on 

 the development of leaves' (1871)^ Starting from the facts discovered by himself 

 and by Kraus that cells have the same size in small etiolated leaves as in large 

 leaves of the same species grown in light, he concludes with justice that the number 

 of cells is larger in the normal than in the etiolated leaf, and that the size of leaves 

 is proportional to the number of cells in them. But from this he draws the following 

 erroneous conclusion : — ' The leaf grows so long as it produces new cells ; and the 

 growth of the leaf does not depend on the increase in size of the cells.' It should 

 rather be, — * The growth of the leaf depends firstly and directly solely on the increase 

 in size of the cells, and is proportional to this ; but the cells, when they have grown 

 larger, divide so that they are actually of about the same size in the small etiolated 

 as in the large green leaf.' He continues : — ' Leaves do not grow in the dark because 



* Gerland (/. c. p. 609) has also arrived at a similar conclusion. 



^ Famintzin, Melanges phys. et chim., Petersbourg iSdS, vol. VII, On the action of light on 

 the cell-division of Spirogyra. 



'^ Batalin, Bot. Zeit. 1871, p. 670. 



