ANALYTICAL CLASS-BOOK OF BOTANY. 



31. Forms of the Cell. — Very young plants, 

 whatever they are destined to become, contain only the 

 rudiments of fibre ; and their whole substance may be 

 said to consist of roundish or oval cells, as you have seen 

 at fig. 6. But as the adjacent parts multiply and enlarge, 

 the cells, being compressed on all sides, assume a twelve- 

 sided form, and in the mass have the appearance of an 

 irregular honeycomb. This is well shown in the highly 

 magnified section of Elder pith, fig. 7. There is a great 

 variety in the forms of the cell, and some of them are 

 extremely elegant. When subjected to pressure on two 

 Opposite sides, they become flattened. This form uni- 

 versally occurs in the cells of the outside integument, or 

 skin, of plants. A row of these flattened cells may be 

 seen at the upper and under surfaces of the Melon leaf, 

 fig. 6, and also in the bark and some other parts of the 

 section of wood, fig. 2. Sometimes the cells assume the 

 appearance of prisms or cylinders ; here they are spindle- 

 shaped, there they are drawn out into long tubes or flat 

 filaments, and again they become stellate, and take the 

 shape of beautiful little stars. 



32. Life op the Cell. — The cell walls, though 

 entirely closed, are penetrable by liquids, and through 

 them every cell sucks up as much as it needs of the nu- 

 trient matter that surrounds it. This being acted on 

 by the vital forces, a chemical change ta,kes place, and a 

 separation occurs. The nutritive portion is taken up for 

 the nourishment and support of the tissues, while the 

 remainder is expelled, as useless. In these acts the life 

 of the cell essentially consists ; and the life of the whole 

 plant, which is but an aggregation of cell lives, can be 

 but a repetition of the same processes. 



33. Gkowth of the Cell. — The nutrient matter 

 thus absorbed is applied to the interstices of the cell 

 walls, which, if no obstacle intervene, extend themselves 

 in all directions, until they reach a definite size, when 

 they are either absorbed by new cells, or they remain 

 permanently fixed. Having once attained to a full 

 growth, their vitality gradually diminishes, until at 

 length they cease to have any part in the actions of life. 

 Each individual cell may be considered as an independent 

 organism, having its own particular life, which it may be 

 said to support by its own labor ; and though, like the 

 Corals, Sponges, and some higher animals, the Cells live 

 in a community, yet each of them, so long as it exists, 

 always maintains its own individual life, character and 

 action, truly as any of these. 



34. Multiplication of Cells. — When the nutrient 



Forms of the cell. Life. Growth. Multiplication. The two modes. Describe. 

 What may an individual Cell be considered ? Instances of rapid growth Par- 



material has accumulated in a sufficient degree for the 

 support of the new cells, they immediately begin to be 

 formed. There are two principal modes of cell forma- 

 tion — first, by partitions, and secondly, by gemmation, or 

 BUDDING, from the free extremity. 



(1.) By Partition. — The cell lining is infolded, 

 until its extending edges meet and cohere, when a double 

 wall of cellulose is deposited, to strengthen and sustain 

 the new structure. Thus two, four, eight, or even a 

 greater number of Daughter-cells are formed, while gene- 

 rally the Mother-cells are absorbed in the new growth; 

 but sometimes they remain. 



(2.) Gemmation. — In this form there is a regulai 

 growing point, from which buds are protruded. Some- 

 times the cells thus formed are again multiplied by par- 

 tition, and thus both modes are combined. Some of the 

 microscopic plants that develope in fermenting infusions, 

 as the Yeast plant, are said to grow by gemmation, 

 while in many of the fresh-water plants known as Con- 

 fervas, both forms are observed. The production of new 

 cells sometimes goes on with inconceivable rapidity 

 This may be seen in the rapid growth of the common 

 Mushrooms, which are composed entirely of cellular 

 tissue. These frequently spring up and grow to the 

 height of several inches in a single night ; and in one of 

 them it has been computed that twenty thousand new 

 cells are formed every minute ! The growth of Mush- 

 rooms, like all vegetable growth, consists entirely of a 

 multiplication of cells. 



35. Parenchyma. — Cellular tissue collectively is 

 called Parenchyma, and sometimes it is convenient to 

 have this distinctive term. When the cells are equally 

 flattened on all sides, as in the pith of Elder, fig. 7, 

 the parenchyma is complete ; when they are not sub- 

 jected to equal pressure, as in the Melon leaf, fig. 6, it is 

 incomplete. 



36. Origin of the Cell. — This is not, as yet, 

 very clearly established ; but a certain little body 

 termed the nucleus is supposed to play an important 

 part in the process, because in the structure of cells it is 

 seen that the particles arrange themselves around this 

 as a common centre. It is not, however, always present. 

 In fig. 5 are represented two cells of the Snowberry, each 

 with its nucleus, a. There are also various currents to 

 be seen, either proceeding from or toward the nucleus, 

 their direction being indicated by arrows. These cur- 

 rents are, without doubt, a result of the vital action in 

 the azotized semi-fluid lining of the cell wall, by which, 



enchyma. When complete ? Incomplete ? Origin of the Cell. "What im- 

 portant part ? Is it always present ? 



