OF THE ELEMEXTAET STEUCTUHES. 



733 



Flowering or Flowerless, are produced and increased; — all 

 increase in the mass of the different organs is therefore due to 

 its agency. The manner in which it takes place is as follows :— 

 the primordial utricle or the protoplasmic lining of the cell 

 — which must be in a perfect condition — becomes gradually 

 constricted on all sides {Jig. UQl,a,b, c, d), folding inwards, in 

 Fig. 1101. 



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,& 



~-i?i 



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Fig. 1101. a. Cell of Conferva glomerata, -nrith the cell-contents con- 

 stricted by the half-completed septum, h. A half-completed septum 

 In-nhich a considerable deposition of cellulose has already taken place, 

 c. A septum in course of development, after the action of an acid, which 

 has caused contraction both of the primordial utricle (,«) and the cell- 

 contents (,&). d. Complete septum split into two lamellce by the action 

 of an acid. After ilohl and Henfrey. 



a sort of hour-glass contraction, and ultimately coalescing and so 

 dividing the original primordial utricle and contained protoplasm 

 into two distinct portions. Each portion of the primordial utricle 

 then secretes a layer of cellulose over its whole surface ; where 

 this is in contact with the original wall of the primary cell it 

 forms a new layer interior to it, but where away from the 

 wall, at the new septum, a distinct cell-wall ; so that the par- 

 tition is double. The original cell thus becomes divided into 

 two, each of which has the power of growing until it reaches the 

 original size of its parent, and then either, or both, may again 

 divide in a similar manner. Cell-division is best observed in 

 water-plants of a low grade of organisation {fig. 1101) and in 

 hairs. In very simple vegetables, such as Falmella, also, in 

 which the newly formed cells separate and become independent 

 plants, the process of division is well seen, but in the higher 

 plants, where they remain permanently united to form tissues of 

 greater or less solidity, it is with difficulty demonstrated. 



In this mode of cell-formation, it is by no means evident what 

 function the nucleus performs. That it is unimportant is clear, 

 because cell-division, as above described, may take place, as it 

 does in some of the lower orders of plants, without the presence 

 of that body. In the higher orders of plants, however, the 

 original nucleus of the cell appears to undergo subdivision into 

 two halves, as is the case with the other contents, so that a 

 nucleus is thus formed for each new cell into which the parent 

 cell has been divided. In other cases, however, separate nuclei 

 are formed for the secondary cells, instead of the original 

 nucleus dividing into two. 



