Morphological Comparative Study On The Flower Bud Differentiation And Flower Development Of Four Species Of Calycanthaceae

Calycanthaceae plants are relict plants of the Tertiary period.They have a very old origin and have a long history.Calycanthaceae plants are all shrubs.Calycanthaceae is a discontinuous distribution between North and South temperate zone,between East Asia and North America.Among,Calycanthus chinensis and Chimonanthus genus are native to China,and both the second class rare and endangered plants in China,and they are both excellent ornamental plant and have a wide range of applications.As flowering plants,the flowering time of Calycanthaceae plants are quite different.C.chinensis blossomes at the end of April and the beginning of May,while most of Chimonanthus plants blossom in October.In particular,Chimonanthzus praecox blossomes in late December,which is different from most plants.In order to find out the reasons for the difference in flowering time among Calycanthaceae plants,it is necessary to compare their flower bud differentiation and flower development from the morphological point of view.In this study,flower buds at different time of four species of the family Calycanthaceae(C.chinensis in Calycanthus.Chimonanthus salicifolius,Chimonanthus nitens and Ch.praecox in Chimonanthus)were studied.We observed anatomically them with the optimized paraffin section technique and light microscope to understand the whole process of flower bud differentiation and flower development in Calycanthaceae,and to determine the stage and morphological characteristics of flower buds at different time.And we recorded the bud length,bud width and external characteristics of flower buds and compared and analyzed the differences of flower formation stages and time between the four species.This study is expected to provide morphological basis for the future studies on the cultivation,flowering regulation,flower fonnation mechanism of the family Calycanthaceae and the reasons for flowering time differences among different species.The main conclusions of this study are as follows:1.The flower fonning process of C.chinensis can be divided into seven stages:flower induction stage,flower initiation stage,bract stage,tepal stage,stamen stage,pistil stage and flower development stage.The flower forming process of Chimonanthus can be divided into six stages.There is no bract stage compared with C.chinensis.2.Although the flowering time of C.chinensis,Ch.salicifolius,Ch.nitens and Ch.praecox are very different,they are all the current-year differentiation type,and the time of their flower bud morphological differentiation is near.The flowering time of C.chinensis was 5～8 months earlier than that of the plants of the genus Chimonanthus,but the time of start the of morphological differentiation of C.chinensis was only was only about 1-2 months earlier than that of them.The flowering time of Ch.praecox is about 2 months later than that of Ch.salicifolius and Ch.nitens,but the time of the initiation of it is ear,but its initiation time is one week earlier than that of Ch.Salicifolius and about one month earlier than Ch.nitens.3.It took only about 45 days from morphological differentiation to flowering in C..chinensis while nearly 6 months in Ch.salicifolius,more than 5 months in Ch.niters,and about 8 months in Ch.praecox.The main reasons for the difference were as follows:(1)the morphological differentiation and flower development speed of the C.chinensis was faster than that of the plants of the genus Chimonanthus.And in C.chinensis the whole process of the morphological differentiation lasted for about 3 weeks,while nearly two months in Ch.salicifolius,about three months in Ch.nitens,,and about 5 weeks in Ch.praecox.After the formation of anthers and ovules,The rate of female and male germ cells differentiation and flowering of C.chinensis was also faster than of plants in the genus Chimonanthus.It took only half a month from anther formation to flowering in C.chinensis,while one month in Ch.salicifolius and Ch.nitens,and 3 months in Ch.praecox.(2)there was no dormancy in C.chinensis.After the morphological differentiation of plants in Chimonanthus was completed,the flower buds would be dormant.At this stage,the growth of flower buds was very slow,and the size of buds was almost unchanged.Among,the dormant period of Ch.praecox was the longest.Ch.praecox had formed mononuclear pollen grains before October 24th,and the pistil matured later than the stamen.4.The length and width of the flower buds of C.chinensis always kept increasing in the whole process of flower bud differentiation and flower development.The length and width of the flower buds of the three species of the genus Chimonanthus maintained an increasing trend before flower initiation.The length of the buds kept increasing during the process of flower bud morphological differentiation,but the width of the buds didn’t change.After the formation of pistil primordium and before the formation of anther and ovule,the length and width of the buds were nearly unchanged.Since anther and ovule was formed until flowering,the length and width of buds both increased rapidly.