HISTOLOGICAL STRUCTURE OF MOTILE ORGANS. 



633 



tissue s projects in both halves beyond the strand. If the observations are carried 

 out in the way here described, the parts cut out of the organ must be laid in 

 water on a glass plate, in order to avoid drying up, since that would destroy 

 the turgescence and tissue-tension. That the relations described exist in the living 

 organ in exactly the same way, however, is at once perceived on making proper 

 sections through such an organ still attached to the stem. 



It will certainly not be superfluous to illustrate the relations of organisation 

 again in the case of Oxalis. Fig. 370 shows a leaf, at / with its three leaflets 

 in the diurnal position, at 2 in the nocturnal position. Further description of 

 these is unnecessary. It is noticed, however, that the motile organs which connect 

 the three leaflets to the top of the petiole are in this case very small, and in 



Fig. 372.— Longitudinal section of the motile organ H i o! a leaflet of Oxalis carnea. ~" 



fact broader than they are long. The transverse section of such an organ is 

 represented in Fig. 371, somewhat highly magnified: beneath the epidermis 

 there is here again a relatively thick mass of parenchymatous tissue, which has 

 distinct intercellular spaces only between the cells of its innermost layers ch : its cells 

 contain chlorophyll-corpuscles as in the swelling tissue of the Bean, and in other such 

 cases. Within the vascular bundle-sheath s lies the axial strand G, which here also is 

 to be regarded as a union of numerous vascular bundles running together in the 

 petiole and separated in the laminae. Here, also, this strand consists of thick-walled, 

 very firm, but by no means lignified tissue ; since it is important that while it is very 

 elastic, it shall yet be exceedingly flexible, for it has to undergo very strong curvatures, 

 both towards the upi)er and towards the lower side, according to the degree of 



