ON GROWTH AND EXTENSION IN THE VEGETABLE KINGDOM. 31 



bundles of vessels, a layer of angular cells, distended trans* 

 versely, of different sizes and crowded without order, filled here 

 and there with small granules, which turn brown but not blue 

 with iodine. Above this layer in the leaf, as well as under it in 

 the bulb-trunk, there appear angular cells considerably larger, 

 not extended transversely, and full of larger granules of starch, 

 which turn blue with iodine. The layer of small, transversely 

 distended cells is therefore clearly the last formed, as it is from 

 this point that proceeded the whole growth of the leaf. The 

 stretching of the cells is here by no means so great as in the 

 roots of the hyacinth, so likewise the growth of the leaf is much 

 slower than that of those fibres. The change in the granules of 

 the cells during the growth of the leaf is curious, first into 

 granules of starch, and then where the leaf becomes green into 

 granules of chlorophyll. 



But whence arise these young cells, which have stationed 

 themselves here in a layer between the old ones, or the smaller 

 cells in the root fibres of the hyacinth which have formed above 

 the root-point? Most probably they arise from an exsuded muci» 

 laginous or, at any rate, not a pure water fluid, by means, in my 

 opinion, of n kind of organic crystallization. In favour of this 

 opinion an experiment can be readily made on willow twigs, 

 when they shoot forth roots in water. As soon as the root-points 

 have protruded from the bark of the root, they are seen to be 

 covei'ed over with a transparent mucilage, which under the 

 microscope consists of cells distended in their length ; and these 

 may be observed as they surround the root-points, and afterwards 

 scale off'. The cells are rounded at the ends where they are not 

 connected v.'ith others ; they often contain cell-granules, some" 

 times none, and round about may be seen a turbid, mucilaginous, 

 unformed mass. Under these cells, nearer the axis, the cells 

 are shorter, broader in the middle, and narrowed at the ends. 

 Here also cell-granules are often present, though sometimes there 

 are none. Comparing this with the end of the hyacinth root at 

 the point where it scales off", v/e observe on the surface of the 

 latter also long, narrow, loosened cells, rounded at the ends, and 

 similar to the supei'ficial cells of the willow rootlets grown in 

 water, and most probably generated in the mucilage exsuded 

 from the underlying, very diffierently formed cells. 



bundles of vessels wind through the cellular tissue in various directions, 

 whilst in the true stem they go directly upwards. This bulb- trunk is 

 covered with a thin coating of cellular tissue, like a kind of bark, through 

 which the root-fibres penetrate downwards with their bundles of vessels, 

 and upwards a few single bundles of vessels enter into the scales of the bulb. 

 These scales are the sheaths of the leaves, which persist and become fleshy 

 after the upper portion of the leaf has withered — a phenomenon which it ia 

 well known does not occur in other kinds of leaves. 



