Abstract
The panicles of rice plant grow very slowly in the dwarf types AAbb, aaBB and aabb as well as in the normal type AABB till about thirty-seven days after the sowing, and there is practically no difference between their sizes in any types before this stage of development.
In fourty-four days after the sowing, the panicles of two larger types AABB and AAbb begin actively to develope and differentiate the branch primordia of the first order. In the other types aaBB and aabb any apparent change is not yet to be found.
The branches of the second order in panicles appear in all types in about fifty days after the sowing.
On these branches the primordia of lemma and palea are formed in the larger types AABB and AAbb, but not yet in the dwarfs aaBB and aabb.
In the following ten days, a perfect set of the flower organs, viz. stamen, filament, pistil, ovule, and lodicule is formed. The length of panicles in this stage of development is apparently larger in the types AABB and AAbb than in those of aaBB and aabb, but the flower size developed at the top of panicles is nearly equal to each other in plants of all genotypes concerned. The fact shows that the longitudinal growth of panicle is controlled at an early stage of development by the dwarf genes, while the eventual difference in flower size among the different types may only appear when the most active growth of glumes proceeds.
It is concluded that so far as the early stages of development concerned, the length of panicles in larger types is caused by the more active cell divisions and the more advanced development of cells so formed and not by the larger dimensions of cells.
