SCIENCE- GOSSIP. 



take on a definite arrangement, that tliey are elon- 

 gated radially, and are only separated by thin lines 

 of ground tissue. As we proceed still nearer to 

 the outer edge we see the ground tissue to be com- 

 posed of thin-walled, rectangular, radiatmg lines 

 of cells, among which fibro-vascular bundles in 

 course of formation may be observed. In this 

 rectangular tissue cells in a state of active 

 division can be seen, and these form the circular 

 cambium layer, the result of whose activity is the 

 •definitely-arranged tissues ju.st described. Outside 



peridtrn-) I jOood 



eliole. A 1 M' /, 



TS. 



DcK-^ma. 



Fig, 3. Twig and Leaf-stalk of Horse-chestuut. 



the cambium we come to the cortex, composed of 

 rounded or elliptic cells, certain of which contain 

 raphides or crystals, here composed of oxalate of 

 lime. Outside the cortex we arrive at the cork 

 cambium, and the regular di\isions of the active 

 cell can be seen bounded by the original epidermis, 

 whose work is now completed. Where the outer- 

 most tissue is ruptured by the increasing thickness, 

 we find the wound closed with corky cells. Indeed, 

 cork seems to be one of Natixre's favourite plasters 

 for injured tissue, and the study of her method of 

 healing, even in the vegetable world, is very 

 interesting. Pores or lenticels may be noticed 

 pi'ojecting from the cork, and it is at the base of 

 these lenticels that the cork fij-st originated. 

 Lenticels are to the maturing plant what the 

 stomata were to the herbaceous stem. 



Tnig and tno leaf-stallis of Horse-cliestnut 

 (L.S.). — The absciss tissue is a corky layer which 

 is found at the point where the petiole artic\ilates 

 with the stem, and effects a complete division 

 between stem and leaf. It cuts through the 

 fibro-va.scular bundles of the petiole, and, its cells 

 being weak, the weight of -the leaf and the action 

 of the winds combined soon tear the leaf from 

 its position, the line of fracture being the "absciss" 

 or " separating layer." This tissue does not ap- 

 pear till all the stock of nourishment has been 

 withdrawn from the petiole, and \mtil after the 

 leaf has ceased to functionate. Probably few 



trees could compete with the horse-chestnut in a 

 •' defoliation " race. The accompanying di-awing 

 (tig 3) represents longitudinal and transverse 

 sections showing the position of the various tissues, 

 the fibro-vascular bundles of the petioles being 

 omitted to simplify the figures. 



Stem of Puiiipliin (L.S.). — The areolated sieve- 

 plates can be seen very plainly when they have 

 been pressed out flat, but they are mostly seen 

 with only the edge presented to the observer, 

 showing the thick callus and the string of proto- 

 plasmic mucus or slime which, broadening at the 

 end, almost covers the plate. "When living, this 

 protoplasm is diffused in the sieve-tube, and its 

 shrinkage is due to alcoholic treatment. Quotmg 

 from M'Alpiue (') : — " The albuminoids, the imme- 

 diate agents in the production of living protoplasm, 

 circulate in well-defined traits through the best- 

 protected portion in the whole plant. This is the 

 soft bast placed between the hard bast on the out- 

 side and the wood on the inside. The cells are of 

 two kinds, according as the albuminoids are dif- 

 fusible or indiffusible. Both are provided with 

 very delicate walls ; but in the one case there are 

 actual holes in the walls, and the indift'usible stuff 

 can be bodily transported, like the blood corpuscles 

 in the stream of the blood. The cells of the soft 

 bast conveying the soluble albuminoids are called 

 ' cambiform'; the others, from their perforation, are 

 known as sieve-tubes." The " cambiform " cells 

 are also known as companion cells, and in the T.S. 

 show as smaller elements, and often look as though 

 tlie}^ had been cut off from the sieve-tubes. 



Stem. of Vegetable Marrow (T.S.). — The fibro-vas- 

 cular bundles are here arranged in two more or less 

 concentric cu'cles, usually containing five bundles 

 in each, but their number and development vary 

 considerably. These bundles are types of the '• bi- 

 ■ collateral " system : they contain two basts, one on 

 the outer and one on the inner confines of the 

 wood. This distinguishing character is common 

 to most of the Cucurbitaceae. The bundles contain 

 a cambium which sometimes becomes inter- 

 fascicular, but the range of its activity is very 

 limited. The whole vascular system is enclosed 

 in ground tissue that is strengthened by a scleren- 

 cbj^ma sheath stronaiylignified. Outside this sheath 



Fig. 4. Stem of Vegetable Marrow. 



is a band of collenchyma, a cellulose, chlorophyll- 

 containing tissue stx'ongly thickened at the corners 

 (fig. 4). The greatest interest, however, lies in the 

 splenclid development of the iDlatesof the sieve tubes, 

 those elements of the phloem that in transverse 

 sections show the largest mesh, whilst the plates 

 are best seen in longitudinal sections. The dotted 

 ducts are amongst the largest known. 

 (1) " Life Histories of Plants." 

 (?b he contimKcl.) 



