ON GBOWTH AND EXTENSION IN THE VEGETABLE KINGI>OM. 35 



SO that they were formerly taken for real holes, and thence arose 

 the names of pores, porous cells, and porous vessels. Mohl first 

 showed that they were not holes, but only light spots. The 

 remaining contents of the cells, the scattered granules, and the 

 cellular nuclei are contained in a second membrane (the inner 

 membrane), which attaches itself to the outer one at the light 

 points, and thus overlays the cellular deposit. This membrane, 

 which Hartig has called the falten-haut, or folded membrane 

 (ptychode), and Mohl the primordial utricle, I should simply 

 term the imier membj-ane. It is easy to obtain a good idea of 

 the structure of cells, by making a fine section of some not very 

 dense part, and steeping it in nitric acid, then washing it in pure 

 water, and applying iodine. In a very successful preparation of 

 a slice of a leaf of the leek (Allium porrum), cut parallel to the 

 surface, and treated as above, we see the cellular membrane with 

 the regularly arranged projections on the inner surface (the cel- 

 lular deposit), and the intermediate thin parts (the so-called 

 poi-es) not coloured by the iodine. Inside the outer membrane of 

 the cell is the inner membrane, with its contents condensed and 

 coloured brown ; and we see plainly that it has extended to the 

 thin parts, and covered the raised parts of the inner surface or 

 cellular deposit. When, as often happens, the nitric acid has 

 not been strong enough to separate the inner membrane from the 

 outer, so that it still spreads over the cellular deposit, this also 

 appears to be coloured brown ; but I cannot state for certain 

 whether this matter also does not with age undergo some 

 change, by which it turns brown with iodine. Sometimes the 

 cellular deposit lies in several layers, and these are often so mul- 

 tiplied as to fill nearly the whole cell. They tiius become gra- 

 dually smaller towards the centre of the cell ; and the filled-up 

 and hardened cell assumes a regular, almost crystalline, appear- 

 ance. Such cells constitute the kernel or pntamen of stone 

 fruits, and the stony parts in pears ; and it is not therefore to be 

 wondered at that cultivation may have influence upon these cells, 

 and diminish their natural cohesion, as in the case of soft-shelled 

 almonds. 



That organic as well as inorganic bodies are generated by 

 crystallisation has already been often suggested, not without foun- 

 dation. But by crystallisation we must understand a natural 

 phenomenon brought about by a symmetrical process, in con- 

 formity with a specific plan. The process itself cannot be 

 explained, but serves to explain the chief phenomena in organic 

 bodies. What writers have called disruption, separation, pre- 

 cipitate, in organic bodies, is almost always to be attributed to 

 this power. The crystal forms, according to its nucleus, in a 

 moment. Three weeks are required for the crystallisation of the 



D 2 



