41 



BOTANY 



cytoplasmic filaments, which proceed from the boundary layer of the 

 cytoplasm and are known as plasmodesms ( 3S ). Such filaments are 

 mostly confined to the pit membrane (Fig. 41 s), but may also 

 penetrate the whole thickness of the cell wall (Fig. 42 pi). The 

 existence of these connecting filaments of living substance between 

 the protoplasts confers an organic unity on the whole body of the 

 plant, serving for the conduction both of substances and of stimuli. 



4. Cell Fusions. Rapid transport of substances within the body 

 of the multicellular plant is necessary, for instance from one organ 

 to another, as from the leaves 

 to the roots. The process of 

 diffusion through the cell walls 

 or the movement of substances 

 in the very fine plasmodesms 



di 



\ 



FIG. 41. A cell from the cortex of the 

 Mistletoe (Viscum album) ; the protoplast 

 has been properly fixed and stained and 

 the wall (m) swollen. The pit membranes 

 (s) are traversed by connecting threads ; 

 ch, chloroplasts ; n, nucleus, (x 1000. 

 After STRASBURGER.) 



FIG. 42. A, A swollen portion of cell wall 

 from the endosperm of the Vegetable Ivory 

 Palm (Phytelephas macrocarpa). At s, s, 

 simple pits filled with cytoplasm ; in the 

 intervening pit membrane are fine connect- 

 ing threads (plasmodesms) ; pi, other threads 

 traversing the whole thickness of the wall, 

 (x 375.) B, The contents of two opposed 

 pits and the connecting threads of the pit 

 membrane, (x 1500.) C, the opening of 

 a pit and the connecting threads of the 

 pit membrane viewed from ' the surface. 

 The smaller circle indicates the canal of the 

 pit, while the larger circle is the pit mem- 

 brane; the dark points on the latter are 

 the plasmodesms. ( x 1500. After STRAS- 

 BURGER.) 



does not suffice to meet this need, even when assisted by the presence 

 of the pits, which have been seen to correspond in the walls separating 

 adjoining cells. The cavities of many cells, especially those which 

 serve for transport, therefore become continuous by relatively wide 

 openings, so that they form tubular structures or CELL FUSIONS. 

 Such openings arise singly or in numbers by a solution of the cell-wall 

 substance, especially in the end walls of adjoining cells. 



5. Formation of Intercellular Spaces and the Ventilation of the 

 Tissues. Usually as the meristematic cells are transformed into 

 permanent tissue and the cell walls thicken, the middle lamella splits 



