MECHANISMS FOR CONVEYANCE TO AND FRO. 481 



Both of the experiments described only exhibit the results mentioned when 

 perforiiR'd on plants, the whole of whose soft bast bundles lie outside the cambium 

 ring, since interruption of the sap-current by ringinj; only takes place under these 

 conditions. If plants are experimented on which possess internal bundles of soft 

 bast in addition to those lying near the surface, as in Tecoma, Thunbergia, and 

 many others, the ringing does not have the result described, because the inner 

 bundles of soft bast (being protected by the hard wood) are not cut through by the 

 knife, and cannot be compressed by the ligature. It should, however, be observed 

 that even in woody plants, whose soft bast lies entii-ely outside the cambium ring, 

 this result is restricted to the year in which the ringing or ligaturing was 

 performed. In consequence of the absence of supplies of albuminous materials 

 through the soft bast, the portion of the branch below the cutting or ligature 

 becomes unhealthy, its cortex dries up and dies, and the disparity between the two 

 portions lying above and below the ringed cut or the tight ligature usually 

 occasions the death of the whole branch tampered with in the following year. 



In the tubular conducting mechanisms, especially in the laticiferous tubes, which 

 are entirely free from transverse M'alls, and also in sieve-tubes, in which perforated 

 horizontal walls are inserted here and there, a transport of substances en masse 

 may occur, but this is impossible in those conducting apparatuses consisting of rows 

 of cells whose length is usually only three or four times their width. In these 

 tracts of cells the numerous non-perforated jDartition-walls of the adjoining cell- 

 chambers are interposed, and must be passed through by the travelling materials. 

 Whether this passage through the walls be regarded as a diosmosis or a filtration, 

 it is at least certain that solid bodies of definite form cannot ti-averse the walls. 

 Even starch-grains of the smallest diameter are alwaj's much larger than the 

 interstices which we imagine to exist in every cell-wall between the groups of 

 molecules; and therefore it follows that even the tiniest visible bodies must always 

 remain behind, as on a filter, in one of the two adjoining cell-chambers, that is to 

 say, on one side or the other of the dividing partition-wall. Accordingly, only fluid 

 materials travel through such cell-tracts as serve for the conduction of substances 

 in the soft bast, parenchyma, and in the bundle sheath. If solid substances take 

 these routes, they must be first brought into a soluble condition. This applies 

 especially to the starch-grains which play such an important part in the life of 

 plants, and not only share in the formation of cellulose, chlorophyll-corpuscles, and 

 fats, but are also heaped up in the storehouses of the plants as materials well suited 

 for storage during the summer drought or through the winter, for use in the next 

 period of vegetation. They ai-e also given to the seeds which have to lead an 

 independent existence, as the first food for the journey after leaving the parent plant. 

 If starch-granules are to travel through the cells of the bundle sheath, composed of 

 hundreds of single ceils, they must be dissolved a hundred times, and a hundred 

 times reformed. It has been definitely proved that this transitory starch is not 

 liquefied at the beginning of its journey and again formed into solid only when it 

 has reached its destination, but that, as stated, a liquefaction, ami after it has 



Vol. I. 31 



