Resumo em Português:

No gênero Aloë, tôdas as espécies estudadas citològicamente até o presente (cêrca de 90) têm 2n = 14 cromossômios. Em uma forma não classificada, a microsporogênese e a gametogênese foram detalhadamente estudadas. O fato mais interessante constatado é o de se associarem, nos grãos de pólen, os núcleos vegetativo e reprodutivo, sem, contudo, se fundirem. Nos tubos polínicos êles de novo se separam, e o reprodutivo dá formação a dois gâmetas. O número e a morfologia dos cromossômios foram estudados em raízes e em grãos de pólen : o complemento cromossômico é constituído por quatro pares de cromossômios longos, bem identificados, e três pares de cromossômios curtos. Um dos cromossômios longos possui um satélite distal; um dos cromossômios curtos possui um satélite proximal, porém apenas em um dos elementos. Um máximo de três nucléolos nos núcleos somáticos de raízes foi constatado, concordando com a existência de três cromossômios com satélites. O fato de ser esta forma heterozigota, para um dos pares de cromossômios curtos, indica que se deve tratar de um híbrido. O estudo botânico revelou que ela apresenta alguns caraterísticos de A. macracantha e outros de A. saponaria. Da espécie A. macracantha, sabe-se apenas que tem sete pares de cromossômios. A. saponaria, com igual número de cromossômios, é uma das três únicas espécies estudadas que possuem satélites no par de cromossômios curtos. Pode-se, então, deduzir, com relativa segurança, que A. saponaria é uma das espécies que entram na constituição desse híbrido. A outra espécie, muito provàvelmente, será A. macracantha.

Resumo em Inglês:

In this paper the results are presented of a study of microsporogenesis and gamete formation in an unclassified form of Aloë. This form of Aloë was found to have 2n = 14 chromosomes, a condition which is characterestic of all of the species of this genus that have been examined cytologically. The most interesting observation made in the present study was the constant association, but no fusion, of the vegetative and reprodutive nuclei inside the pollen grain. It was also noted that this association disappears when the nuclei enter the pollen tube. The reproductive nucleus in the pollen tube gives rise to two small male gametes. This paper also includes a description of the morphology of the chromosomes as studied in the root tip cells and in pollen grains. In the form of Aloe studied there are 4 pairs of long chromosomes and 3 pairs of short ones. One pair of the long chromosomes was found to be homozygous for a satellite at the distal arm and one pair of short chromosomes was determined to be heterozygous for a satellite at the proximal arm. It was also observed that there was a maximum of three nucleoli in each somatic cell nucleus which agrees with the existence of three satélites. The cytological observations made indicate that the Aloë plant studied is a hybrid. Also a botanical analysis revealed that this form of Aloë has some characters of A. saponaría (one of the few species with satellites in short chromosomes) and some characters similar to those of A. macracantha. On the basis of the present investigations then, it seem highly probable that the form of Aloë studied is a hybrid between the two above mentioned species.

Resumo em Inglês:

The present paper reports the results of general studies undertaken to determine the relative importance of soil moisture and light on symptom expression of the tristeza disease. It also includes data on the effects of the disease on transpiration and chemical composition of infected plants and records the results of attempts to inactivate the tristeza virus in budwood by means of hot water and chemical treatments. In the present tests, using potted plants, tristeza disease symptoms were observed to occur eight to ten weeks after inoculation on plants maintained in standing water and on those having a daily application of 200cc of water. In contrast to this relatively rapid and positive symptom expression, it required 28 weeks before definite advanced tristeza disease symptoms were recognized on the inoculated plants given only 50cc of water daily. Under continuous heavy shade conditions the healthy and inoculated plants showed practically no growth and no tristeza disease symptoms. The growth of the healthy plants increased with the increase in periods (6, 10, and 14 hrs) of exposure to daylight while the inoculated plants grew as well as the healthy plants for the first month they subsequently practically ceased growth. The results of the tests on the influence of light and soil moisture show that conditions favorable for rapid plant growth also favor early symptom expression of the disease and that stunting of the plant is one the principal characteristics of the tristeza disease. The data obtained from the transpiration studies show that under the controlled test conditions the transpiration of the healthy plants was two and a half times greater than that of the tristeza diseased plants. The study of chemical composition of the plants indicated that there were some differences in the percentages of CaO and Na(2)0 in the leaves and stems of diseased and healthy plants. The data also indicate that, although the differences in the amount of chemicals present in the root systems of diseased and healthy plants were comparatively small, in all cases except for MgO the quantities were larger in the healthy than in the diseased roots. Under field conditions, nutritional deficiency symptoms have been associated with initial tristeza disease symptoms following plant inoculations. Early tests with applications of minor elements indicated some beneficial effects from applications of zinc sulphate. Under controlled conditions in the screenhouse, however, no beneficial effects were obtained from spray applications of zinc sulphate on inoculated plants. Attempts to inactivate the tristeza virus in budwood sticks that were immersed in hot water were ineffective at the four different temperatures and fourteen exposure periods tested. The results obtained suggest that the thermal-death-point of the virus is probably higher than that of the living cells of the budwood, and that treatment by hot water does not appear to be a feasible method for inactivation of the virus in living budwood. Chemical inactivation of the tristeza virus was tried using nine different chemicals at four dilutions for each. Under the conditions of the tests none of the chemicals employed appeared to have any inhibiting effect on the tristeza virus.

Resumo em Inglês:

Only one plant of Coffea arabica L. var. rugosa K.M.C., is available for study Its fruit production is very low. Of the progeny observed, none has reproduced th rugose condition of the leaves characteristic of the parent plant. Previous study ha shown that the rugose condition of the leaves could not be considered a somatic chimer because the tissues have a normal number (2n=44) of chromosomes. The present cytological study was undertaken in order to find out if the low yiel of the rugose variety could be related to abnormalities in microsporogenesis. The structure of the chromosomes in early prophase is difficult to study. In diaki nesis two pairs and sometimes three pairs of chromosomes appear to be attached to th nucleolus. Also in diakinesis it is possible to locate the centromere in the chromosoni pairs and to count the chiasmata. It was observed that an average of 6.6 bivalent show one single chiasma, 12.3 bivalents show two chiamata and 3.0 bivalents shoM three chiasmata. The average total number of chiasmata per cell at this phase is o 40.0, while at metaphase this number is reduced to 34.7. The first division in the mi crospore is normal and the resulting two nuclei differ in size and also in the size o their nucleolus. The polen grains are normal, giving 69% germination on a medium containinj 0,5% of agar and 15% of sucrose. It is concluded that microsporogenesis is normal and would not appear to be relate< to the low production of fruits of the rugosa variety. The fact that none of the progen¹ has reproduced the rugose condition might be due to the limited number of plants observed.