Retrospective Criticism. sis 



" 15. It would appear, from the case of the purple laburnum, that a true 

 mule or hybrid cannot always be propagated with certainty, even by portions 

 of the plant, or by what is called extension ; since it never can be certain 

 "whether the portion taken off for propagation will produce the mule or one 

 of the parents. As it is uncertain what are, and what are not, very distinct 

 species, many of the plants originated by cross-breeding, and considered mules, 

 may in reality not be so ; and may, consequently, prove permanent and im- 

 proved varieties. Some mules, also, such as that between the sweetwilliam 

 and the common pink, are much less liable to degenerate than others. As 

 some of the most beautiful and useful plants in cultivation are cross-bred 

 varieties or mules, particularly among geraniums, heaths, roses, gloxinias, &c, 

 the subject well deserves the attention of the amateur, who will find it a 

 source of useful amusement and recreation." 



Is not the purple laburnum from a bud that sprang at the edges of the 

 insertion between bud and stock ? It was said to be this, and not from seed. 

 If so, it is not a seedling hybrid or mule. 



[The true origin of the purple laburnum, in our opinion, is given by M. 

 Camuset, in our Volume for 1841, p. 398., viz, that it is a hybrid between a 

 laburnum and Cytisus purpureus.] 



" 103. Growth In general, the roots of plants are not furnished 



with buds, and hence roots cannot be used in propagation in the same manner 

 as branches ; nevertheless, there are numerous exceptions ; and some extensive 

 orders of plants, such as the itosaceas, Campanulaceae, Cruciferae, and some 

 of the Amentaceae, have roots abounding in adventitious buds ; and if these 

 roots are cut into portions, and planted in the soil with the part of the root 

 which was next the stem uppermost, and their points exposed to the air, or 

 very slightly covered, they will produce plants. This, however, is never the 

 case with the roots of annuals or biennials ; and hence, in Cruciferae, while 

 the common sea-kale produces buds in abundance from the cuttings of the 

 roots, the same thing never takes place in the common cabbage. The nature 

 of plants in this respect is very different ; for while the fasciculated tubercles 

 of the dahlia, if deprived of the plate which produces the buds, have no power 

 of originating fresh buds, yet the tubers of the common pseony, so treated, 

 produce them freely." 



It may be questioned whether the roots of .Rosacea?, &c, abound in adven- 

 titious buds. It is more likely these buds are called into existence by an 

 effort of the vitality of the plant. In such as the i?hus, Papaver, &c, which 

 abound in a thick viscid sap, the very smallest pieces, in which it is scarcely 

 possible buds could be formed, are found to produce them, if they have only 

 fibres to collect nourishment. The buds are generally formed at the edges of 

 the cut, where the leaf is extravasated, showing they are formed from the 

 extravasated sap, and did not previously exist in the state of buds. The edge 

 of the cut is sometimes so crowded with buds, that they cannot be sup- 

 posed to have had preexistence in such large quantities. The buds noticed 

 at 121. may be more properly called axillary than adventitious. 



" 128. The art of causing plants to produce flowers sooner than they would 

 do naturally is one of great importance to the cultivator. The principle on 

 which it is founded seems to be that of causing a greater accumulation of 

 nutritive matter in the particular part of the plant intended to produce 

 flowers than is natural to that part ; or, in the case of annual plants, to con- 

 centrate the nutritive matter of the entire plant, by growing it in a drier 

 soil than that which is natural to it. Hence, by ringing any particular branch 

 of a tree, blossom-buds will be formed on the part of the branch above the 

 ring, while shoots more watery than usual will be formed below it. Hence, 

 also, by grafting a shoot from a seedling tree on the extremities of the 

 branches of a full-grown tree of the same species, blossoms will be produced 

 some years sooner than would have been the case had the branch remained 

 on its parent plant. In this way new kinds of fruit, raised from seed, may be 

 proved much sooner than if the seedling plants were left a sufficient number 



3d Ser.— 1842. X. ll 



