Vol. 44 TORREYA April 1944 



Improved Rooting of Cryptostegia Cuttings Gallused on the Plant 



H. F. L.OOMIS 1 AND J. H. Heuer 2 



Vegetative propagation of plants of the first generation hybrid between 

 Cryptostegia grandiflora and C. madagascariensis, having superior rubber con- 

 tent of leaves or high latex yield, is essential for increasing stocks of selected 

 plants. Standard types of stem cuttings collected in various ways, subjected to 

 different treatments, including the use of many growth promoting substances 

 of various strengths, have been tried. The results indicate that with almost any 

 type of material or treatment rooting takes place more rapidly and extensively 

 where bottom heat can be applied in the propagating box and maintained at 

 temperatures of 85° to 90° F., with the tops of the cuttings exposed to mate- 

 rially lower temperatures. During the summer such conditions cannot be main- 

 tained and rooting results generally have been much less satisfactory. Under 

 the best conditions root production has been slow and, only in cuttings treated 

 with Rootone or talc dust containing 1000 p.p.m. of naphthalene acetic acid or 

 naphthyl acetamide, has the percentage with strong roots and satisfactory leaf 

 development been fairly high. 



Air-layering or marcottage of branches directly on the plants has been 

 found a fairly satisfactory means of propagation. A relatively high proportion 

 of the treated branches take root and the roots are stronger and more vigorous 

 than are developed by most types of cuttings under the best treatments. Chief 

 objection to the marcottage method is its cost in labor, material, and time. 



In marcottage of Cryptostegia stems, the first step is the removal of a com- 

 plete ring of bark one to two centimeters in length at the base of the portion to 

 be rooted, being sure that no cambial tissue remains to bridge the girdled area. 

 Such girdling does not kill the stem above it and several weeks after the mar- 

 cotte box is applied a callus forms and roots may be expected to appear some- 

 what later. The success of this girdling method with marcottes suggested that 

 girdling of stems from one to ten days before making cuttings might cause 

 better and more prompt formation of roots on the cuttings, but extensive trials 

 showed no advantage of such treatment over cuttings not previously girdled. 



In harvesting these girdled stems for cuttings, or in the girdling of stems 

 for marcotting, some were overlooked and remained on the plants without 

 further attention. Several months later it was observed that these girdled stems 

 were still alive and that a large callus had formed on each at the upper edge 

 of the girdled area at what would have been the bottom of the cutting. Five 



1 Senior agronomist, Division of Plant Exploration and Introduction. 



2 Principal scientific aid, Rubber Plant Investigations, Bureau of Plant Industry, Soils 

 and Agricultural Engineering, Agricultural Research Administration. 



