89. Campion flower shows proportional growth of ligule and petal.

90. Snowball plant. Observe form of leaves. Upper leaves are entire, the older leaves lower down the stem are indented.

The ratios of growth of parts in a leaf are not similar as growth of the leaf proceeds.

91. Water ranunculus plant. The aerial and aquatic leaves are very different in form or in the ratios of their growth.

92. Wall-flower. Two sets of stamens of different lengths; two forms of proportional growth of anther and filament are presented.

93. Bigonia leaf, asymmetrical; there is not the same amount of tissue on either side of mid-rib.

94. Laurel leaf. Symmetrical.

95. Convolvulus, stem with leaves near apex. Two leaves were killed in early spring and remain attached. The specimen shows that individual leaves alter in form or proportions of growth as they advance.

96. Buds of sycamore showing proportions of scales and leaves as growth advances.

97. Buds of chestnut.

98. Flower-bud-development of Models. See Sachs. 99. Ovule and its coats: development of-Models. See Sachs.

Examples showing some Sequences of Proportional

Growth.

100. Calvaria of children, from birth till twelve months old, showing the actual increase of size of the fontanelle during early growth, and later its gradual closure.

101. A series of pelves at successive ages, showing increase of size, and change of shape of foramina as growth proceeds.

102. Model of stoma of a leaf, showing that variation in the size of the guard-cells regulates the size of the opening.

103. Leaves of cactus, showing that the ratio of parenchyma and vascular tissue is such as to make the leaf succulent.

104. Leaves of holly. The hard character of the leaf is due to the small amount of parenchyma. Mus. Cat. Gen. Pathol. 121.

105. Fruits of acacia, in various stages of development, showing air-cavity in the seed-case, owing to proportional growth of seeds and pericarp.

106. Casts of the vertex of the skulls of infants at various ages from birth upwards, showing variation in fontanelle.

107. Fruit of chestnut at various stages. The ratios of growth of carpel and seed is such that no vacant space is developed.

108. Pea fruit. Carpel grows in such ratio to seeds that an air space may exist around them.

109. Nigella fruit. Carpel has split into two layers, of which the outer has grown more than the inner, leaving an air space between them.

110. Bladder acacia fruit. Carpel has grown more than seeds, an air-containing cavity results; it follows that the fruit is light and easily carried by the wind.

111. Poppy fruit. Styles are not developed till fruit is ripe, when their growth elevates the stigma and makes a porous dehiscence.

112. Ash buds. The protection which results from these ratios of growth is seen, and exposure of leaves to light follows.

112 a. A germinating seed. The seed consists of the Anteceembryo enclosed in its testa, or covering. As long as it dents of growth. is dry no change occurs; when moistened and kept at a sufficient temperature the process of germination begins by the swelling and growth of the embryo. But the testa does not grow; it may stretch a little, but soon the increased size of the embryo causes the seed-case to split. The splitting of the testa is the outcome of unequal increase in the size of the embryo and the seed-case. It thus differs essentially from the growth of fruits.

Sequence

The sequences of proportional growth may be to produce of growth. cross-fertilization in flowers, as is well illustrated by the growth of a flower of the Compositae.

In the flowers of the Composite order a special arrangement is found with regard to the relative growth of the stamens and the pistil, which results in cross-fertilization of the flowers; that is, the flower being hermaphrodite is not self-fertilized. The stamens, being united by the margins

Fig. 13.-Compositae.

of their anthers, form a tube, into which the pollen is discharged. The stamens grow to their full height and maturity before the pistil, which, during the early stage of the flower, is short and immature. When the anthers are ripe and have filled their tube with pollen, the style begins to grow, and passes up the tube formed by the anthers, pushing the pollen powder before it, which now accumulates in a heap at the top of the anther tube. Later, the continued growth of the style brings the stigma as the most

prominent part of the flower; its lobes open and expose the receptive surface. An insect visiting the flower in its early condition, meets with a heap of pollen dust at the top of each floret, and thus dusts its abdominal surface; when the insect later on visits a flower in the later stage of growth, with the style protruded and expanded, it deposits some pollen from the former flower upon the prominent and receptive stigma.

Specimens showing Growth controlled by pressure or mechanical strain.

113. Part of the stem of a plant that has grown bent, owing to its having been strained constantly in one direction.

a.

Fig. 14. Solanum jasminoides.

One of its petioles clasping a stick.

b. Transverse section of leaf-stalk not pressed by twig.

c. Transverse section of young leaf-stalk which has clasped a support. After C. Darwin.

114. Leaf and petiole of a climbing plant (Solanum jasminoides); the petiole being greatly thickened from pressure of the twig around which it is coiled. "The flexible

petiole of a half or a quarter-grown leaf which has clasped an object for three or four days increases much in thickness, and after several weeks becomes so wonderfully hard and rigid, that it can hardly be removed from its support. On comparing a thin transverse slice of such a petiole with one from an older leaf growing close beneath, which has not clasped anything, its diameter was found to be fully doubled, and its structure greatly changed 1."

115. Head of femur with trochanters, and muscles attached to it. The portions of bone most pulled upon have grown the most prominent.

116. Specimen.

117. Specimen.

118. Foot of Chinese woman, much distorted, atrophied, and hindered in growth by artificial compression. Mus. Cat., Gen. Pathol., 30, Royal College of Surgeons.

119. Specimen.

120. Specimen.

121. Specimen.

122. Specimen.

123. Clematis glandulosa. Two young leaves have clasped two twigs, and the clasping portions have become thickened. C. Darwin. Climbers.

A. Tendril fully de

124. Ampelopsis hederacea. veloped, with a young leaf on the opposite side of the stem. B. Older tendril, several weeks after its attachment to a wall, with the branches thickened and spirally contracted, and with the extremities developed into discs. The unattached branches of this tendril have withered and dropped off. C. Darwin. Climbers.

125. Rattle grass2 developes suckers on the roots where they touch the living roots of neighbouring grass, and live on them as parasites. Prof. Trail.

126.

Vitis hatarinphylla suckers develope when they press on objects.

1 C. Darwin on Climbing plants.

2 Rheanthus Christa galli.