942 



THE NATURE BOOK 



PATCHES OF SPORANGIA ON BACK OF MALE FERN. 



Even with this arrangement the dis- 

 tribution covers a much wider area 

 than might be thought possible. A 

 strange form of seed dispersion is that 

 to be seen in the case of the Earth Nut 

 {Arachis hypogcva). The singular part 

 about this plant is that, as the seeds begin 

 to ripen, the pods are forced below the 

 surface of the soil through the lengthening 

 of the flower stalks, and are in this way 

 actually planted. The same method has 

 been adopted by the Sweet Violet, and 

 also in the case of a few other plants. 

 Tile phenomenon is certainly rather a 

 puzzling one, for the behaviour of these 

 species can scarcely be said to aid in 

 the wide dispersal of the plant. In some 

 of the instances which possess this strange 

 habit, there are, in addition to the sub- 

 terranean pods, aerial ones which bear 

 their seeds in a more ordinary manner. 

 We may suppose that the seeds which are 

 so carefully sown by the plant are put 

 into position in order to make quite certain 

 that the species shall continue to hold its 

 own on that particular spot. 



The large number of plants which do 

 not produce flowers make comparatively 

 httle provision for the welfare of their 

 offspring. The early observers were much 

 puzzled as to how it was that Ferns which 

 appeared never to produce seed were able 

 to increase their kind. It was not until 

 the coming of the microscope that the 

 strange life history of the Fern was under- 

 stood. An examination of the brown 

 patches to be found on the back of many 

 Fern fronds shows them to be groupings 

 of .strange little stalked cases, called 



sporangia. At a certain stage in their 

 existence these sporangia burst open, and 

 scatter their contents to the winds of 

 heaven. This matter is formed of 

 numbers of individual grains, in form 

 varying largely in the different species. 

 These spores are very different in their 

 formation from the seeds of flowering 

 species ; each one is Uttle more than a 

 speck of hfe in an elementary form. 



Although the process of development 

 from the spore to the Fern plant varies 

 considerably, a t}^ical case may be briefly 

 outlined. Being very light, the spores 

 float away on the shghtest breezes and a 

 certain number of them are sure to find 

 a resting-place on some moist patch of 

 soil. It is not very long after the lodg- 

 ment of a spore that a change takes place, 

 wliich by a process of cell extension results 

 in the production of a heart-shaped green 

 film in measurement about an eighth of 

 an inch. After an interval, two very 

 distinct kinds of cells begin to put in an 

 appearance upon the under-side of the 

 prothallium. These represent respectively 

 the archegonia, or germ cell, and the 

 antheridia, or sperm cell. At a certain 

 stage in the history of these cells, thread- 

 like processes, known as antherozoids, 

 emerge from the sperm cells and enter 

 tlie germ cells, and thus bring about the 

 fertihsation of the embryo. Soon after 

 tliis has been accomplished the prothal- 

 lium and all its system of cells dries 

 up, leaving behind only the fecundated 

 germ. Yet another change, and the tiny 

 frond struggles upwards, and the birth 

 of tlu- Fern is an accomplished fact. 



