FRUITS REPLACED BY OFFSHOOTS. 45^ 



Cirsium heterophyllum and spinosissimum, and Cirsium afftne, a hybrid between 



a heterophyllum and C. oleraceuvi, are very abundant in many Alpine valleys, 



and one may find more examples of these hybrids than of their parents in many 



a meadow. Several of the Fuller's Thistle hybrids, the parents of which are 



biennial, become perennial by a production of lateral shoots from the leaf-axils at 



the base of the stem. Here also, as with climatic conditions, we find vegetative 



propagation replacing fruit-production. 



I There are also many species, of which it cannot be definitely asserted that 



I they have arisen by hybridization in recent times, which fruit but seldom even 



I when the climatic conditions are in every way favourable for this kind of repro- 



j duction. According to agriculturists, there are many kinds of Potato which flower 



! only occasionally but do not ripen fruit, although the flowers and pollen-grains 



i appear quite normal. It is just these Potatoes which are characterized by their 



I rich production of tubers, fruit-formation being in them replaced by vegetative 



j propagation. 



i That plants, with double flowers, the ovaries of which, under the influence of 

 j little insects (Phytopus), have undergone a deep-reaching transformation, should 

 ripen no fruits is to be expected and has long been known, as also is the fact that 

 ! these plants produce buds and offshoots freely. Of special note in this connection 

 is a Bitter-cress (Cardamine uliginosa) often met with in damp meadows in the 

 neighbourhood of Vienna, Salzburg, and Ried, growing wild with double flowers. 

 On most of the plants, the fruits of which are abortive, those curious leaf-buds, 

 represented in fig. 200 *, p. 41, are to be found. 



Again, with many species of plants, it may come to pass that the insects which 



should accomplish their pollination are now no longer prevalent in the region 



where the plants grow, or indeed have entirely deserted them. This category of 



plants obviously includes only such forms as are destitute of arrangements for 



promoting autogamy, in the case of cross-pollination not taking place. In a very 



considerable number of these plants, flowers and fruits are replaced by offshoots — 



offshoots of the most varied kinds, including aerial and subterranean tubers, 



bulbils, green leafy shoots, and, in rare cases, little bud-like structures, from each 



of which a thick, fleshy root arises in such a manner that the greater part of the 



offshoot consists of a root. 



I As all these varieties of oflfshoots will be dealt with in a later chapter devoted 



' to the distribution of such structures by wind, animals, and special mechanisms, it 



i must suffice to speak here of a very few cases. Growing in sunny spots, the 



I yellow flowers of the Lesser Celandine (Ranunculus Ficaria) are occasionally 



I visited by little pollen-eating beetles, by flies and bees; under these circumstances 



! heads of fruit are ripened here and there from the flowers. But in shady places, 



j beneath bushes, and on the dark forest floor, these insect-visits are much rarer, 



; and almost all the flowers fail to ripen fruit. These shaded plants, however, 



I develop little bulbous bodies in the axils of their upper foliage-leaves, which 



I become detached on the withering of the shoot and give rise to new plants (see 



