Jan. 29, 1885] 



NA TURE 



291 



the freshly-collected materials I used alcohol, osmic or 

 picric acid ; all the observations described below were 

 made upon fresh material, treated, after fixing for a few- 

 minutes, with strong or dilute sulphuric acid, so as to 

 swell the cell-walls. 1 The fresh material was first cut in 

 alcohol (or osmic or picric acid) ; the sections were 

 then for a short time placed in a drop of sulphuric acid, 

 and washed rapidly in a watch-glass with distilled water. 

 After washings in several watch-glasses, the sections may 

 be stained. For staining I first used the saffranine, and 

 later solely the eosine (from Dr. Th. Schuchardt, Gorlitz, 

 Silesia). The eosine has a great and admirably defined 

 selective staining power. It is a very excellent negative 

 reagent for the cell-wall, and when employed with some 

 precautions colours only or almost only the protoplasm. 

 It is however requisite that a dilute solution of the dye 

 should be made (1 part of eosine to 50-60 parts of water), 

 and that the stained sections should be washed carefully 

 (for ten to fifteen minutes) in water. 



That the phenomena detailed below are not artificially 

 produced by reagents is proved in certain instances. The 

 presence of the connecting protoplasmic filaments in the 

 intact (not swollen 1 normal cell-wall or pit-closing mem- 

 brane was witnessed in the medullary cells of the mistle- 

 toe, the sections of which were merely mounted in water 

 and stained with eosine. 



I now proceed to give an account of the results I ob- 

 tained with the various tissues in which the continuity of 

 protoplasm was shown to exist. 



Epidermis, Glaucium Fischeri gave the first results. 

 In the leaf-epidermis the connecting processes of the 

 protoplasms, many in number (one for each pit), are well 

 defined ; the same is the case in that of Yiscum and 

 Loranthus, but in the latter plants the fine connecting- 

 threads were also visible. From the protoplasms of the 

 epidermis-cells radiate numerous processes towards the 

 pits, and in any two neighbouring cells the processes from 

 the one protoplast are exactly opposite those proceeding 

 from the other. All the epidermis-cells, as in Ficus elastic,!, 

 are in direct communication with one another and with 

 the " guard-cells " of the stomata. The same is also 

 the case in epidermis composed of several layers. The 

 connection is very difficult to make out, though visible 

 after a moderate swelling in the collenchymatic-hypoderm 

 (Rhus, Cotinus, Cucurbita pepo, Solanum, Liriodendron, 

 &c). 



The bark-parenchyma is one of the most favourable 

 objects for investigation, and even when the cell-wall has 

 been very conspicuously swollen or dissolved, the connec- 

 tion is unaltered (Loranthus, Yiscum, Abies alba, Picea 

 excelsa, Gingko biloba, &c). When no hypoderm exists, 

 the protoplasts of the epidermic-cells should be directly 

 connected with those of the bark-cells. Such is the case 

 in Yiscum and Loranthus. The epidermal cell-walls of 

 these plants may have undergone considerable swelling, 

 and so the connective processes become very extended, 

 but the fine connective threads are still conserved. In 

 the leaf-parenchyma (Viscum, Loranthus) the connection 

 is very distinct also in the cotyledons of Phascolus multi- 

 florus. It is very difficult to prove the communication in 

 leaves where the parenchyma has been doubly differen- 

 tiated, viz. into chlorenchyma and into pneumo-en- 

 chyma. The medullary-parenchyma of Loranthus or 

 Viscum furnish excellent objects for such investigations ; 

 the fine bent threads (five to eight in number) can be 

 very distinctly examined after a feeble swelling of the 

 cell-wall. In the Conifers I find only the connective 

 processes distinct (Gingko, &c). In the Loranthaceae the 

 communication is to be directly seen between the medul- 

 lary-ray-cells and xylem-cells, between the phloem-ray- 

 cells and bast-parenchy ma ; finally between the medullary- 

 ray-cells and the sclerenchyma-eells [these last are found 



1 See, for details of my method, Zeitsschri/t fur wistensck. Mikrosl.opie, 

 &c, i. ii. p. 301, 1884. 



in the neighbourhood of the xylem (primary) vessels in 

 Yiscum.] 



The bast-fires of Yiscum, Loranthus, are in direct 

 communication with one another, and in Viscum the 

 fibres of the inner-phloem also communicate with the 

 medullary- cells. The communication between cambium, 

 young bast-fibres, and bast-parenchyma, in the Coniferae 

 can be demonstrated only with high powers. The 

 communication and connection of the soft-bast proto- 

 plasts is eminently remarkable. These protoplasts re- 

 main in connection even after total dissolution of their 

 cell-walls (Cucurbita, Coniferae, Loranthaceae, &c). I 

 investigated also the sieve-tubes, and have found that 

 these in their entire length are connected with neighbour- 

 ing sieve-tubes, ox bast-parenchyma-cells, ox collateral cells 

 (Nebenzellen) (Yiscum, Loranthus, Ficus elastica, &c). 

 The connective threads are often strongly developed in 

 Cucurbita. They assume the figure of a compressed 

 sphere. 



Xylem. — I may remark that the details of the xylem 

 communications are very difficult to observe. In general 

 I have studied the communication of the xylem elements 

 best in the Loranthaceae, and especially in Yiscum. The 

 xylem of the mistletoe is composed of libriform cells, 

 compensating cells {Ersatssellen), and vessels. The cell- 

 walls of the libriform cells are very much thickened, and 

 bear pits only on the middle part of the cell. These cells 

 are variously curved and bent, and offer favourable condi- 

 tions for investigation — but then the communication of 

 the libriform cells with one another, libriform cells + com- 

 pensating cells, and of the latter together can be easily 

 seen. In the Coniferae the communication of the xylem 

 elements is only clear in the younger states. In theyoung 

 tracheides the distinct threads could be very clearly seen. 

 In the older tracheides merely a striation (caused by the 

 threads) could be detected through the pit-closing mem- 

 brane). As regards the occurrence of a direct continuity, 

 the xylem vessels gave generally a negative result. Al- 

 though in many instances the occurrence of protoplasm 

 in the great xylem vessels could be demonstrated, still 

 direct communications seemed to me to be extremely 

 rare. I could find this direct connection in one instance 

 in Loranthus. The great (but only the pitted) vessels were 

 here connected with the adjacent cells. 



Finally, the protoplasts of the secretory cells are also 

 in direct communication with the neighbouring proto- 

 plasts, such as in the resin-cannel cells. The cells of 

 the resin-cannels are, in the Coniferae, directly con- 

 nected with the adjacent leaf- or bark-parenchyma, or 

 phyllogen-cells. In the bark of Gingko I was also able 

 to confirm the communication of the crystal-bearing 

 cells (crystal-glands) with the bark-parenchyma cells. 

 I have no doubt that the same structure would be 

 equally well demonstrated in the various secretive cells 

 and vessels. In all the observed cases the communication 

 of adjacent protoplasts is effected by delicate wavy proto- 

 plasmic threads. The connective thread either in a round- 

 about way traverses the sieve-pore pit-closing membrane, 

 or directly traverses the cell-wall when the membrane is 

 unpitted or the pits feebly developed. From a physio- 

 logical point of view the pits form one of the most im- 

 portant arrangements. 



The protoplasts are also in direct connection with the 

 intercellular protoplasm. The intercellular plasm which 

 fills the intercellular spaces was first observed by J. G. 

 Agardh 1 in the Florideae, and by Russow- (1882) in 

 various phanerogamous plants. I have (1S83) also 

 studied (first in the bark of Liriodendron tulipiferd) its 

 occurrence in many phanerogamous plants and published 

 my observations in 1S84. 3 At this time also Berthold 

 published a paper * in which he confirmed its occurrence 



1 L c. , p. 140 &c. _ z L.c, p 350 &c. 



3 In the Magyar XCiCnrtatii Lapck, viii. 1884, pp. 19, 7-4 



4 Berthold, " Ueber das Vorkommen von Protoplasroa in Intercel- 

 n," Berichte der devt* -htn botan. Gesellsch., ii. iS?4, i. p. 20. 



