CELL MARKINGS. 25 



the characteristic patterns presented by the cell-wall due to 



internal thickening may be mentioned the following : spiral, 



when the thickening matter is deposited in the form of a 



continuous spiral band; annular, when arranged in the 



form of closed rings. Transitional forms unite the two 



preceding arrangements ; thus it is not unusual to see a cell 



with spiral markings passing over into the annular condition 



due to the breaking up of the spiral to form rings ; in these 



two forms the thickening matter often becomes detached 



from the wall and lies perfectly free in the cavity of the cell, 



and being more or less elastic, protrudes in the form of a 



loose spiral coil when the cell-wall is torn ; if a leaf or 



fiower-stalk of the common hyacinth or rhubarb is notched 



all round with a knife through the epidermis or skin, and 



the central portion then gently drawn asunder, a mass of 



very fine cobweb-like glistening threads are drawn out, 



which are collectively strong enough to support the weight 



of the broken portion. These threads are the loose spirals 



that have been drawn out of the broken cells. In the two 



foregoing examples the ornamentation is due to the 



deposited matter, which covers but a comparatively small 



portion of the area of the cell-wall, whereas in the following 



cases, where the thickening usually covers the greater 



portion of the surface, the unthickened portions form the 



pattern observable from the outside. Scalariform, when 



the unthickened portions consist of rows of parallel bands 



arranged like the steps of a ladder. This form is characteristic 



of certain tissues of the fern group, without at the same time 



being entirely confined to that group. Pits, or pitted cells, 



are very general, and depend on the thickening matter 



leaving small circular portions of the primary cell-wall 



unthickened. These thin portions were considered by the 



