376 CHLOROPHYLL-GRANULES AND THE SUN'S RAYS. 



on by the green tissue of the aerial roots. Green tissue is much more frequently to 

 be met with in stem-structures than in roots. Hundreds of rushes, bulrushes, 

 cyperuses, and horse-tails, as well the Casuarineae and species of Ephedra, included 

 under the switch plants, many papilionaceous plants of the genera Retama, 

 Genista, and Spartium, a number of Salicomias, tropical orchids, and cactiform 

 plants, the Duckweed (Lemna), and all the plants possessing flattened shoots (see 

 tig. 82), contain green tissue, without exception, in the cortex of their stem and 

 branches. Also ovaries and fruits which are not yet fully ripe are so universally 

 coloured green that in popular language green fruit and unripe fruit are synony- 

 mous. Chlorophyll is more rarely observed in seeds. Those whose embryos are 

 differentiated into axis and leaf only seldom — as, for example, in the pines — show 

 green tissue in the cotyledons. The seeds of orchids, especially those living 

 epiphytically on the bark of trees, behave in a peculiar manner. These are 

 marvellously small, consist of only a single group of parenchymatous cells, and no 

 trace is to be seen in them of a radicle or cotyledon. They only retain the capacity 

 of germinating a short time, and it is important to these seeds, which are poorly 

 supplied with reserve food, that immediately after leaving the fruit-capsule they 

 may be able to provide themselves with nourishment from their surroundings, and 

 to manufacture organic substances from this food. This they can naturally only do 

 by the help of chlorophyll, and it is interesting to notice that they also are actually 

 endowed with this substance. Even when they are still inclosed in the capsule of 

 the parent plant these seeds become green, and when they are carried by the wind 

 into some cleft on the bark of an old tree-trunk the chlorophyll is able at once to 

 function. After a short time a small green tubercle grows out of the green seed, 

 and fixes itself by absorbent cells to the substratum, then very gradually it grows 

 up to form a large plant-stem. 



Large flowers whose petals, from the commencement to the end of the flowering 

 period, exhibit a green colour are -esteemed rarities. On the other hand, small lie >ml 

 leaves, rich in chlorophyll, are of very common occurrence. The change of the 

 floral colour also, during the flowering period, from white, red, violet, and brown, to 

 green, has been frequently observed in small as well as in fairly large flowers. A 

 very striking example of this is the Black Hellebore (Helleborus niger). When its 

 flowers open, the outer large leaves situated below the petals (which are transformed 

 into small nectaries), are snow-white, and show up conspicuously from their darker 

 surroundings. From afar they attract the attention of honey-collecting insects, by 

 whom they are eagerly sought out. When, by means of these honey-sucking 

 insects, pollination is brought about, the small nectaries, as well as the large 

 dazzling-white outer floral leaves called sepals, become superfluous. The nectaries 

 forthwith fall off, but the large sepals remain and take up another function. 

 Chlorophyll is abundantly developed in their cells; the white colour disappears; 

 fresh green appears in its stead, and the same floral leaves which previously had 

 attracted insects by their conspicuous colour now function as green leaves exactly 

 like foliage-leaves. A similar alteration of colour, which also has the same 



