32 ON GKOWTH AND EXTENSION IN THE VEGETABLE KINGDOM, 



An evident formation in mucilage, and by means of the 

 mucilage, is shown in the nmcilaginous exsiidations of many 

 fruit-coatings, as is so well represented by Mr. C. F. Schmidt in 

 plate 7 of the ' Anatomy of Plants.' When we moisten with 

 water under tlie microscope the slender membrane which clothes 

 the caryopses of some species of Salvia, we suddenly see pro- 

 truded a number of long spiral threads, or rather spii-ally-twisted 

 threads, such as we see in spiral vessels, surrounded with 

 mucilage, or sometimes with a very fine membrane, so that the 

 exsudation looks like a spiral vessel. Sometimes also granules 

 of starch are scattered in it. It is true that we see alreatly in 

 the dry cells indications of spiral coils, but on immersion a spiral 

 vessel is formed of such a length that it is impossible to assume 

 so complete a pre-existing formation in the cells themselves. At 

 any rate, it strikes the eye that the spiral thread has liere been 

 generated in the mucilage. " 



It is known that in our dicotyledonous trees a new layer is 

 formed every year between the wood and the bark constituting 

 tlie annual ring. It is an old opinion, that between the wood and 

 tlie bark a generating sap, the cambium^ is exsuded, from Avhich 

 the new layer of wood is formed. In fact, we find in spring, 

 when the trees are forming tlieir leaves and in full sap, and the 

 bark separates readily from the wood, that there has exsuded 

 from Ihem a moisture, wliicli is indeed the cause of the bark sepa- 

 rating so readily from the wood. It is also prolmble that this 

 moisture contributes at least to tlie formation of tlie new layer 

 of wood, if it does not entirely generate it. It appeared, there- 

 fore, advisable to examine under the microscope this generating 

 sap during the time of its formation ; but it is very difficult to 

 procure it pure. If a thin slice is taken from the wood, or from 

 the bark, the already-formed portions of wood or bark predo- 

 minate so much that it is impossible to ascertain clearly what 

 there may be in the generating sap. If we scrape off the sap, 

 the small particles contained in it are thrown into confusion, and 

 crushed together. The only course is gently to press the fap on 

 to a piece of glass, and immediately to moisten it with water, in 

 order that it may not dry up ; then under a magnifying power 

 of 600 diameters we see a number of granules, of a form more 

 or less globular, of very different sizes, and all uniform inside. 

 The sm.allest granules have in water the molecular motion which 

 is observable in all very small and fine granules belonging to or- 

 ganised m.atter. These granules are more or less densely crowded 

 in different shrubs or trees — very close, and often adhering in 

 rows, in the cambium of the hazel-nut ; less crowded in the ash ; 

 least of all in the willow. Amongst these granules we see single 

 cells, also of different sizes, but always much larger than the 



