July 1951 School Magazine

July. 1951

Brisbane Girls' Grammar School Mag azine

July, 195!

:Brisbane Girls' Gramma' Sch ool Mag azine

into four parts; from the first part the root is formed, from the second the leaf and stem and the other two unite to develop into the foot by which the younger fern is connected to the prothallus . Ferns can occasionally arise by budding from the prothallus or directly from_the fern without the form- ation of spores. The spores are generally shed in early sum- mer after which the spore bearing leaflets wither and fall off. The form and arrangement of spore cases and the pres- ence or absence of a protecting membrane are used to class- ify ferns into families, the largest being the polybody which includes most of the common species and is characterized by the leaves which are usually intricately divided. In the tropics abound the greatest variety as well as the largest ferns. These are the tree ferns having erect, woody, unbranched stems ressembling the trunks of palm trees. The trunk is formed by the coalesence of the bases of the leaf stalks. At the top of the trunk grow huge, wide spreading, compound leaves which sometimes have petioles as large as a man's arm and often grow to a length of ten to seven- teen feet. When these leaves die and fall they leave scars on the stem. In temperate regions most ferns have stems which grow at .or just below the surface of the soil and from these stems grow hairlike adventourus roots and very large leaves, which are the only visible parts of the plant. Bracken is a species of tall coarse ferns usually found in temperate regions growing in woods and clearings but is also often abundant in sandy regions. In some p laces the leaves form dense undergrowth. Usually the leaves are short but an increase in the richness of the soi~ brings about a proportional increase in their height. The stem of the bracken grows a. few inches below the surface and is long slender and sparingly branched, the anterior end being the growing region. When the progres- sive death and decay of older parts extends to where branch- ing has taken place, the branch becomes separated from the main stem and under favourable conditions will continue growing as an indepedent plant. In this manner the num- ber of plants is greatly increased. As the stem elongates it gives rise to many adventourus roots which are long and occasionally branched. During the spring and summer months as the plant resumes its growth a new group of adventourus roots are formed. Each leaf begins its growth at the growing tip of the stem developing underneath 24

the ground but as the lower part of the petiole becomes elongated it pushes the tightly coiled leaf bud up into the air and once there the bud begins to unroll. This develop- ment of the leaf is characteristic of nearly all ferns. The mature bracken leaf is composed of a slender petiole with a much divided blade. On the central axis of the plant are two rows of primary leaflets, one on each side of the axis, the lower pair being the largest and the others grad- ually becoming_smaller. Several pairs of the lower leaflets may be divided but the r: ·mall upper ones are usually not divided. All bracken leaves are green and look exactly alike but . on examining them closely it can be seen that some bear sporangia and some do not. In bracken the sporophyll man- ufactures food as well as the sterile leaves. The sori of bracken are found along the margins of the leaf. The other different species of ferns differ in details of form and structure but mainly in the sporophyte. This dif- :!erence is most noticeable in the shape of the leaf blade. One of the most simple types of blade is that of the walking fern which is a long elongated triangle. An interesting feature of this fern is the fact that many of the blades keel over to touch the ground where it may give rise to a new plant. In this way the number of plants is increased and also gives the fern its name. Another type of fern with an undivided leaf is the "harts tongue". Some ferns such as the polybody have simple but deeply lobed leaf blades. One such member of this class is the maiden hair whose fragile branched frond bears small lobed leaflets of varying size. Some ferns such as the Christmas fern have once compound leaves while others such as th& royal fern and lady fern have twice compound leaves, for here many of the primary leaflets are divided into secondary leaflets. The Royal fern is one of the finest British species sometimes reaching a height of eight to ten feet. This is sometimes thought to be a flowery fern for the pinnules at the top when converted to spores cases ressemble small brown flowers . The asparagus is a flowering fern in which the leaves are reduced to minute scales and the visible part of the plant is thick green shoots tearing small pink berries which later open into pink flowers before forming red berries. The asparagus is however not a tree fern. The sporangia of these ferns unlike those of bracken are

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