THE LIVING PLANT. 



29 



The mass or substance of a plant is spoken 

 of as tissue ; if of unmodified cells, the tissue is 

 cellular; if of vessels and fibres, it is called 

 fibro-vascular tissue (fig. 23). The most simply 



Fig. 23.— Cut illustrating various tissues. To the left Spiral Vessels, fol- 

 lowed by long Conducting Cells. These are succeeded by Cellular 

 Tissue or Parenchyma. In some of the square cells are Crystals of 

 Oxalate of Lime. In the longer cells are groups of Needle-like Crystals 

 called Raphides. To the extreme right are Pitted Cells. 



constructed plants are those consisting of one 

 cell, which may be either simple or branched. 

 Next come plants that consist of many cells 

 associated into a tissue ; and then those in which 

 vessels are found together with cells. Those 

 plants that have no true roots, leaves, or flowers, 

 are cellular plants, devoid of vessels in their 

 composition. Those plants that have well- 

 marked roots, leaves, or flowers, have also 



vessels, and are hence called vascular plants, 

 such as a fern, a lily, or an oak. So that a mere 

 glance, without a microscopical examination, is 

 generally sufficient to enable the observer to 

 know whether he is looking at a cellular or at a 

 vascular plant. 



The Thallus. 



The aggregation of cells to form an individual 

 plant is termed a thallus, and those plants which 

 consist wholly of cells are termed TAallophytes or 

 Thallogem. The thallus may consist of long 

 threads or hyphce, simple or variously branched, 

 as in the spawn of a mushroom; or it may con- 

 sist of flat plates of leaf-like appearance and 

 texture, as in many sea-weeds. [m. t. m.1 



CHAPTER II. 



THE LIVING PLANT. 



Green Plants — Uncoloured Plants — Parasites — 

 Saprophytes — Microbes — Symbiosis — Thallo- 

 phytes and vascular cryptogams — asexual and 

 Sexual Conditions — Flowering Plants — Sensa- 

 tion and Movements in Plants — Continuity of 

 Protoplasm. 



The plant, then, is unicellular or multicellular. 

 and if its structure remains thus simple it is a 

 Thallophyte. If some of the cells grow into 

 vessels it becomes a vascular plant. Plants may 

 also be distinguished into two groups, those 

 which do not, and those which, under the in- 

 fluence of light and heat, do form a green 

 substance in their cells, this green substance 

 being in the form of granules, often varied in 





jnnonnnr 



Fig. 24.— The woodcuts show the appearance of a section through the Common Duckweed, Lemna trisulca. Above is seen an Epidermis of square 

 cells, without Chlorophyll ; beneath is seen a similar layer constituting the Lower Epidermis or Skin. Between the two skins is the Cellular 

 Tissue, consisting of two layers of large square cells iu which the Chlorophyll Granules are differently arranged, according to the direction and 

 intensity of the light : 1, in darkness ; 2, in direct sunlight ; 3, in diffused light. 



position according to the direction of the light, 

 and technically known as chlorophyll (fig. 24). 



Green Plants. — It is the green plants that are 

 the most highly organized and with which the 

 gardener has most to do. The green plants pursue 

 an independent existence, work for themselves, 

 obtain their own food-supplies, elaborate them 

 to supply their own requirements, use up some 

 at once, store up others for future consumption. 



Colourless Plants. — The colourless plants are 

 far less independent. They cannot manufacture 

 their food from the raw material, they must 

 get it ready made, hence they are parasites. 

 living on the juices of other plants, or they are 

 saprophytes, availing themselves, for food, of the 

 decaying or dead tissues of other plants or of 

 animals. They may hence serve a useful pur- 

 pose as scavengers. There was a time when 



