BOTANICAL APPLICATIONS 



Mitochondria. The electron microscope 

 shows that the mitochondria are funda- 

 mentally different morphologically from 

 other cell particles. As in the case of animal 

 mitochondria, those of plant cells show a 

 double-membrane system. Within the mito- 

 chondrion are complex fine structures, the 

 cristae mitochondriales, which consist of in- 



FiG. 14. Shadowed portion of primary cell wall 

 Valonia, X5500. (After Steward and Miihlethaler, 

 courtesy of the Annals of Botany) 



vaginations of the mitochondrial membrane 

 reaching from one wall to the other. These 

 structures are highly variable from cell to 

 cell and between different species of plants. 

 It is now known with reasonable certainty 

 that the mitochondrion is the site of respira- 

 tory activity of the plant. 



The Cell Wall. Many studies of the pri- 

 mary cell wall have been obtained by macer- 

 ating the cells and reducing them to a very 

 thin film. These thin films are in the form of 

 sub-microscopic strands of cellulose which in 

 turn can be split into even finer threads by 

 means of such techniques as ultrasonic irra- 

 diation. The micro-fibrils obtained in this 

 way are elementary in nature because they 

 correspond to the crystalline micellar strands 

 which can be detected by means of x-ray 

 diffraction. It can be seen in Figure 14 that 

 the micro-fibrils of the primary cell wall are 

 interwoven to form a very dense network. 



In the secondary cell wall Avhich consists 

 entirely of micro-fibrils of cellulose, the 

 strands tend to lie parallel instead of in the 

 form of a network as shown in Figure 15. In 

 successive lamellae the orientation of the 

 parallel fibrils is shifted. 



Fig. 15. Shadowed portion of secondary cell wall of Valonia, X11,0()0. {After Steward and 

 Miihlethaler, courtesy of the Annals of Botany) 



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